Valence Band Mixing in GaAs/AlGaAs Quantum Wells Adjacent to Self-Assembled InAlAs Antidots

Kawazu, Takuya

doi:https://doi.org/10.1155/2019/5349291

Journal of Nanomaterials

On this page

Abstract Introduction Materials and Methods Results and Discussion Conclusions Data Availability Conflicts of Interest Acknowledgments References Copyright Related Articles

Research Article | Open Access

Volume 2019 | Article ID 5349291 | https://doi.org/10.1155/2019/5349291

Valence Band Mixing in GaAs/AlGaAs Quantum Wells Adjacent to Self-Assembled InAlAs Antidots

Takuya Kawazu¹

Academic Editor: Leander Tapfer

Received14 Dec 2018

Revised14 Mar 2019

Accepted24 Mar 2019

Published28 Apr 2019

Abstract

Optical properties of GaAs/AlGaAs quantum wells (QWs) in the vicinity of InAlAs quantum dots (QDs) were studied and compared with a theoretical model to clarify how the QD strain affects the electronic states in the nearby QW. In_0.4Al_0.6As QDs are embedded at the top of the QWs; the QD layer acts as a source of strain as well as an energy barrier. Photoluminescence excitation (PLE) measurements showed that the QD formation leads to the increase in the ratio _e-lh/_e-hh of the PLE intensities for the light hole (lh) and the heavy hole (hh), indicating the presence of the valence band mixing. We also theoretically calculated the hh-lh mixing in the QW due to the nearby QD strain and evaluated the PLE ratio _e-lh/_e-hh.

1. Introduction

Molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), and other deposition methods have been significantly developed over a few decades, which have made it possible to fabricate a variety of high-quality quantum nanostructures such as quantum wells (QWs), quantum wires, and quantum dots (QDs) [1]. In particular, much of the work has been done on 10 nm-scale self-assembled QDs in the Stranski–Krastanov (SK) mode due to their ease of fabrication [2–5]. Because of their potential for the advanced photonic device applications including lasers [6], charge storage devices [7–9], and interband and intersubband photodetectors [10–13], the optical and electric properties of self-assembled QDs have been actively studied by using near-infrared spectroscopy [14, 15], capacitance spectroscopy [16, 17], and resonant tunneling spectroscopy [18].

In the SK growth, highly crystalline QDs are spontaneously formed just by depositing source materials on a lattice-mismatched substrate. The SK growth initially proceeds in a layer-by-layer fashion, which forms a thin wetting layer (WL). After the layer exceeds a certain critical thickness, high-density defect-free QDs are coherently formed in order to reduce the strain energy. Therefore, the strain is inevitably present inside and outside the QDs, which strongly affects the electronic states inside and outside them. Many experimental and theoretical works have been done on the QD strain and have clarified the strain effects on the electronic states [19–22].

In this work, we study optical properties of GaAs/AlGaAs QWs in the vicinity of In_0.4Al_0.6As QDs and clarify the effect of the QD strain on the nearby QW. The band gap of In_0.4Al_0.6As is estimated to be about 1.87 eV and is larger than that of GaAs [23–25]. For the case of In_0.4Al_0.6As QDs in GaAs, the energy gap difference will be larger due to the strain. Hence, when In_0.4Al_0.6As QDs are embedded at the top of a GaAs/AlGaAs QW, the QD layer acts as a source of strain as well as an energy barrier, which is a suitable system for the study of the strain effects outside the QDs. By analyzing the PLE spectra and carrying out the theoretical calculation, we here show how the QD strain affects the electronic states in the nearby QW.

2. Materials and Methods

2.1. Composition of AlGaAs and InAlAs

For sample preparation, we employed MBE with the use of a reflection high-energy electron diffraction (RHEED) system. We can explore the growth dynamics of MBE by observing temporal oscillations in the intensity of the specular beam of the RHEED pattern. The intensity of the specular beam changes depending on the surface roughness. Under normal conditions, the crystal growth by MBE proceeds in a layer-by-layer fashion [26]. When a smooth complete layer is formed on the crystal surface during the MBE growth, a maximum intensity of the specular beam is observed. In contrast, the specular beam intensity becomes minimum at half-layer coverage, where 2D nuclei are grown at random positions on the crystal surface. Therefore, the oscillation period of the specular beam intensity precisely corresponds to the growth of a single molecular layer [27]. The analysis of the intensity oscillation has now been used to calibrate beam fluxes, alloy composition, and the thickness of a deposited layer [28].

For MBE of III-V semiconductors, the growth rate is controlled by the group III elements. In addition, when two or more group III elements are simultaneously supplied, their growth rates are additive [29, 30]. By observing the specular beam intensity oscillations during the growths of GaAs and AlAs, we calibrated Ga and Al fluxes so that the deposition rates of Ga and Al are about and monolayer (ML)/s. Hence, the expected Al mole fraction of Al_xGa_1-xAs is [29]. To determine the In deposition rate , we used the specular beam intensity oscillation for the growth of InGaAs by following Ref. [30]: . The expected In mole fraction of In_xAl_1-xAs is then [29].

2.2. Critical Thickness of QD Formation

RHEED is a powerful tool for investigating not only the growth dynamics (Section 2.1) but also the atomic structure of crystal surfaces in situ. At the end of the buffer growth on the (100) surface of GaAs, we clearly observed a streaky reconstruction RHEED pattern, indicating the high-quality crystalline of the buffer layer [26]. When In_0.4Al_0.6As is deposited on the sample surface, the streaky reconstruction changed and its intensity slowly weakened at low InAlAs coverage (<4 ML). In this initial stage, the crystal growth proceeds in a layer-by-layer fashion, and the deposited lattice-mismatched materials form a fully strained 2D layer [3]. For further deposition of 4–5 ML of In_0.4Al_0.6As, a spotty RHEED pattern suddenly appeared, corresponding to the growth of 3D single crystal dots [2, 3, 30]. Therefore, the critical thickness of In_0.4Al_0.6As QDs on GaAs is expected to be 4–5 ML; the QD formation occurs when In_0.4Al_0.6As is deposited above , while a thin 2D layer is formed for the InAlAs deposition below .

2.3. Sample Preparation

For our study, we prepared GaAs/AlGaAs QWs with embedded self-assembled InAlAs QDs on semi-insulating GaAs (001) substrates. The sample structure is schematically shown in Figure 1. First, we deposited a 300 nm thick GaAs buffer layer and a superlattice buffer (14 periods of 13 nm AlGaAs/2 nm GaAs) at the substrate temperature of 570-580°C. Next, a 5 nm thick GaAs layer was grown to form a reference QW for checking the GaAs deposition rate. We then deposited a superlattice barrier layer (7 periods of 13 nm AlGaAs/2 nm GaAs) and a GaAs QW layer (the thickness ). After was lowered to 520°C, InAlAs QDs were formed by depositing 6.1 ML of In_xAl_1-xAs with a nominal In composition of . While was raised to 570-580°C rapidly, we further grew a superlattice barrier layer (14 periods of 13 nm AlGaAs/2 nm GaAs) and a 10 nm thick GaAs capping layer. To investigate the QD shapes and density by atomic force microscopy (AFM) measurements, we formed InAlAs QDs again on the top of the sample under similar condition for the embedded QDs. This sample with embedded QDs is referred to as S.

For comparison, we also grew a sample (C) of the identical structure except that the deposited thickness of InAlAs is about 3.1 ML. In this condition, InAlAs QDs are not formed, since the critical thickness of In_0.4Al_0.6As QDs on GaAs is 4–5 ML.

2.4. PLE Measurements

PLE spectra of the samples were measured in a closed cycle helium cryostat at about 20 K by using a standard lock-in technique. The samples were excited with a Ti:sapphire laser, where the emission wavelength is variable in the range of about 710 to 830 nm. The luminescence was dispersed by a grating monochromator and detected at the lower energy tail of the QW PL peak by using an AgOCs photomultiplier tube. Figure 2 shows the schematic drawing of the PLE measurement setup. The excitation laser enters the sample at an angle of about 45 degrees. Note that the direction of the excitation laser is changed due to the refraction of light, when the laser light enters the inside of the sample. The angle between the excitation laser and the vertical direction of the QW is estimated at about 10 degrees.

3. Results and Discussion

3.1. Surface Morphology

To evaluate the sample surface profiles, we performed AFM measurements in a noncontact mode. Figures 3(a) and 3(b) show the AFM images of the samples C and S; 3.1 ML of InAlAs was deposited on the former sample, while the InAlAs thickness is 6.1 ML for the latter. On the sample C (Figure 3(a)), we do not observe InAlAs QDs but a low height step-terrace structure, since the deposited InAlAs amount is less than the critical thickness (4–5 ML) of the QD growth. In contrast, InAlAs QDs are successfully formed on the sample S, where the QD radius and height are 13 and 2.2 nm, respectively, on average, and the dot density is about .

(a)

(b)

3.2. PLE Spectra

Figure 4 shows the PLE spectra of the samples C and S. While varying the energy of the exciting laser, we observed the luminescence at 1.572 and 1.576 eV for C and S (marked by arrows in Figure 4). The lower energy peaks at about and 1.584 eV for C and S are attributed to the excitation of electrons and heavy holes (-hh), where the full width at half maximum (FWHM) _e-hh is about 3 meV. In contrast, the higher energy peaks at about and 1.607 eV for C and S () come from the excitation of electrons and light holes (-lh). The slight differences of the peak energies stem from a small unintentional change of the GaAs growth rate; i.e., the GaAs QW thickness of C is a little bit larger than that of S, which was noticed by the PL from the reference QW of 5 nm thick GaAs (not shown). Note that the PLE intensity _e-lh of the -lh excitation for S is larger than that for C, although _e-hh is almost the same for S and R. The ratio _e-lh/_e-hh is about 0.5 and 0.65 for C and S, respectively. The larger ratio _e-lh/_e-hh for S indicates the presence of the valence band mixing of the hh and lh states in the QW.

3.3. Excitation Energies of -hh and -lh Pairs

To confirm the assignment of the PLE peaks and also to estimate the experimental error for the QW thickness, we evaluate the excitation energies of the -hh and -lh pairs by using a simple model for a finite barrier QW. According to Ref. [31], the ground state energy of electrons confined in a QW (thickness , barrier height for the conduction band) is obtained by solving where and are Planck’s constant and the electron effective mass, respectively. From equation (1), the ground state energies (, ) of heavy and light holes are also calculated by using the hh and lh effective masses (, ) and the barrier height for the valence band. The calculated excitation energies of the -hh and -lh pairs are and , respectively. The parameters used in the calculation are listed in Table 1. Although we obtain reasonable agreement between the calculated and experimental excitation energies, the experimental values are a little bit larger than the calculated ones. Therefore, we speculate that the QW thickness is slightly smaller (<10%) than the thickness of the designed ones.

3.4. Optical Matrix Element

The PLE spectra are predominantly determined by the optical absorption at the energy of the excitation laser, and the intensity is approximately proportional to the squared matrix element [33, 34]:

Here, is the unit polarization vector and is the momentum operator. is the electron wave function at the Brillouin zone center. In the infinite barrier approximation, where is the periodic part of the -like Bloch function with spin-up or spin-down . is the area of the QW. The -axis is taken to be perpendicular to the QW surface, and the QW is located at the origin. is the hole wave function at the Brillouin zone center and is written as where is the coefficient reflecting the degree of the valence band mixing. The hole state is doubly degenerate and distinguished by . is the Luttinger-Kohn (LK) basis, where indicates the heavy holes (, , ±3/2) and the light holes (, , ±1/2) for the valence band formalism.

The LK basis is isotropic in the - plane apart from the phase factor and diagonalizes the Hamiltonian for holes in the QW on the (001) surface. Therefore, for the QW without QDs, the hole wave function contains only a single component of the LK basis. In contrast, when InAlAs QDs are embedded at the top of the QW, the hole wave function consists of several components of the LK basis (see equation (4)) because of the valence band mixing due to the QD strain.

From equations (2), (3), and (4), we obtain

is determined only by the Bloch functions at the Brillouin zone center and does not depend on the QD strain. Therefore, we can evaluate the valence band mixing due to the strain (i.e., the magnitude of ) by examining the PLE intensity.

3.5. QD Strain Potential and Perturbative Approach

When Young’s modulus and Poisson’s ratio can be considered a constant in the system, the strain is expressed as where is the Lamè displacement potential [35]. By assuming that the height of the QD is written as and by remembering , the two-dimensional Fourier component of is approximately given as [36]

Here, is the Bessel function of the second kind. is the mismatch rate between the lattice constants of GaAs and InAlAs [24]; i.e.,

In this approximation, the piezoelectric potential has the simple form [36]: where and are the piezoelectric constant and the dielectric constant, respectively. From equations (6) and (7), we can easily prove that the hydrostatic strain disappears:

For the potential of the strain effect including piezoelectricity due to the QD located at (0, 0, ), the matrix element between the hole states is given as [37] where and are the deformation potential coefficients. The unperturbed wave function of the hole ground state is defined as where is the positional vector in the QW plain. The ordering of the valence band basis functions in equation (11) is , , , and .

By following the second-order perturbation theory for the QD strain potential in equation (11), the valence band Hamiltonian matrix at the Brillouin zone center is written as [38, 39] where is the density of the randomly distributed QDs. and are given as where and are the electron rest mass and the Luttinger parameter, respectively. The upper and lower signs are taken for the heavy and light holes, respectively. In our case, the first-order perturbation terms vanish because (see equations (12), (13), (14), and (15)). The coefficient can be evaluated by diagonalizing equation (17).

3.6. Calculated Results

Some terms of the squared matrix element in equation (17) disappear by the angular integration. The nonvanishing terms are , , , , and , where is defined as

Because of this, the valence band mixing only occurs between and -1/2 and between and 1/2. Figure 5 shows the nonvanishing terms as functions of the wave number . The parameters used in the calculation are listed in Table 2, and is set to 5 nm. For simplicity, the ternary parameters for In_0.4Al_0.6As are derived from the binary parameters by linear interpolation [40]. Note that all the nonvanishing terms exponentially decrease with the increase in at (: Fermi wave number), indicating that only the hole states near the Brillouin zone center contribute to the perturbative calculation.

Figures 6(a) and 6(b) show the calculated coefficient for the heavy and light hole states as functions of the QD density . Here, the coefficient does not depend on . The valence band mixing occurs between and -1/2 and between and 1/2, which exhibits the same result. Note that the light hole component increases in the heavy hole state as the QD density increases, while becomes large in the light hole state at large .

(a)

(b)

Figure 7 shows the ratio of the squared optical matrix elements for the light and heavy hole states calculated by using equation (5) as a function of the QD density . Here, we take into account the incident angle and the refraction of the excitation light. In Figure 7, we also plot the measured ratio _e-lh/_e-hh of the integrated PLE intensities for the light and heavy holes with open circles, since the ratio is a rough estimate of the ratio _e-lh/_e-hh. Note that the ratio increases with the increase in the QD density , resulting from the heavy and light hole mixing. This trend agrees with the experimental results, which indicates at least partly the validity of our assumption; the valence band mixing in the QW is caused by the nearby QD strain.

Although our model qualitatively explains the experimental results, the quantitative agreement is not satisfactory. One reason may be the simplifications in the model. We ignore the split-off valence bands [34], the excitonic effects [33], and the interface roughness of the QW [41]. In addition, the QD shape is assumed to be a thin sheet, and the strain parameters are approximated to be isotropic [35, 36]. Another reason may be the experimental errors for the thickness of the QW, the compositions of the ternary materials, and also the angle of the incident laser light. Besides, we estimated the diameter and height of embedded InAlAs QDs from the AFM images of QDs formed on the substrate surface. However, the shape of QDs grown in the SK mode often changes during overgrowth [42]. These issues will be left as the subject of a future work.

4. Conclusions

We investigated the optical properties of GaAs/AlGaAs quantum wells (QWs) in the vicinity of self-assembled InAlAs quantum dots (QDs), where the QDs act as a source of strain. We prepared two QW samples with and without the InAlAs QDs by depositing In_0.4Al_0.6As above and below the critical thickness of the Stranski–Krastanov (SK) growth. Photoluminescence excitation (PLE) measurements showed that the InAlAs QDs increase the ratio _e-lh/_e-hh of the PLE intensities for the electron-light hole (lh) and electron-heavy hole (hh) excitations; _e-lh/_e-hh is about 0.65 and 0.5 for the samples with and without the InAlAs QDs, respectively. We also theoretically studied how the QD strain affects the electric states of carriers in the QW. It was found that the QD strain induces the hh-lh mixing, resulting in the increase in _e-lh and the decrease in _e-hh, which partly explains the experimental data.

Data Availability

The data used to support the findings of this study are available from the corresponding author upon request.

Conflicts of Interest

The author declares that he has no conflicts of interest.

Acknowledgments

This research was partially supported by MEXT KAKENHI Grant Number 17K06364.

References

H. Sakaki, “Quantum wires, quantum boxes and related structures: physics, device potentials and structural requirements,” Surface Science, vol. 267, no. 1-3, pp. 623–629, 1992.
View at: Publisher Site | Google Scholar
D. Leonard, M. Krishnamurthy, C. M. Reaves, S. P. Denbaars, and P. M. Petroff, “Direct formation of quantum‐sized dots from uniform coherent islands of InGaAs on GaAs surfaces,” Applied Physics Letters, vol. 63, no. 23, pp. 3203–3205, 1993.
View at: Publisher Site | Google Scholar
J. M. Moison, F. Houzay, F. Barthe, L. Leprince, E. Andre, and O. Vatel, “Self‐organized growth of regular nanometer‐scale InAs dots on GaAs,” Applied Physics Letters, vol. 64, no. 2, pp. 196–198, 1994.
View at: Publisher Site | Google Scholar
S. Ohkouchi and N. Ikoma, “Shape Transition of GaAs Islands Grown on InAs (001) Surfaces,” Japanese Journal of Applied Physics, vol. 33, 3B, Part 2, pp. L470–L472, 1994.
View at: Publisher Site | Google Scholar
R. Notzel, J. Temmyo, H. Kamada, T. Furuta, and T. Tamamura, “Strong photoluminescence emission at room temperature of strained InGaAs quantum disks (200–30 nm diameter) self‐organized on GaAs (311)B substrates,” Applied Physics Letters, vol. 65, no. 4, pp. 457–459, 1994.
View at: Publisher Site | Google Scholar
Y. Arakawa and H. Sakaki, “Multidimensional quantum well laser and temperature dependence of its threshold current,” Applied Physics Letters, vol. 40, no. 11, pp. 939–941, 1982.
View at: Publisher Site | Google Scholar
G. Yusa and H. Sakaki, “GaAs/n-AlGaAs field-effect transistor with embedded InAs quantum traps and its programmable threshold characteristics,” Electronics Letters, vol. 32, no. 5, p. 491, 1996.
View at: Publisher Site | Google Scholar
K. Koike, K. Saitoh, S. Li, S. Sasa, M. Inoue, and M. Yano, “Room-temperature operation of a memory-effect AlGaAs/GaAs heterojunction field-effect transistor with self-assembled InAs nanodots,” Applied Physics Letters, vol. 76, no. 11, pp. 1464–1466, 2000.
View at: Publisher Site | Google Scholar
R. J. Luyken, A. Lorke, G. M. Ribeiro, and P. M. Petroff, “Charging dynamics in vertically aligned InAs quantum dots,” Materials Science and Technology, vol. 18, no. 7, pp. 725–728, 2002.
View at: Publisher Site | Google Scholar
G. Yusa and H. Sakaki, “Trapping of photogenerated carriers by InAs quantum dots and persistent photoconductivity in novel GaAs/n-AlGaAs field-effect transistor structures,” Applied Physics Letters, vol. 70, no. 3, pp. 345–347, 1997.
View at: Publisher Site | Google Scholar
S. W. Lee, K. Hirakawa, and Y. Shimada, “Bound-to-continuum intersubband photoconductivity of self-assembled InAs quantum dots in modulation-doped heterostructures,” Applied Physics Letters, vol. 75, no. 10, pp. 1428–1430, 1999.
View at: Publisher Site | Google Scholar
A. J. Shields, M. P. O’Sullivan, I. Farrer et al., “Detection of single photons using a field-effect transistor gated by a layer of quantum dots,” Applied Physics Letters, vol. 76, no. 25, pp. 3673–3675, 2000.
View at: Publisher Site | Google Scholar
L. Chu, A. Zrenner, D. Bougeard, M. Bichler, and G. Abstreiter, “A quantum dot infrared photodetector with lateral carrier transport,” Physica E: Low-dimensional Systems and Nanostructures, vol. 13, no. 2-4, pp. 301–304, 2002.
View at: Publisher Site | Google Scholar
J.-Y. Marzin, J. . M. Gérard, A. Izraël, D. Barrier, and G. Bastard, “Photoluminescence of single InAs quantum dots obtained by self-organized growth on GaAs,” Physical Review Letters, vol. 73, no. 5, pp. 716–719, 1994.
View at: Publisher Site | Google Scholar
R. P. Mirin, J. P. Ibbetson, K. Nishi, A. C. Gossard, and J. E. Bowers, “1.3 μm photoluminescence from InGaAs quantum dots on GaAs,” Applied Physics Letters, vol. 67, no. 25, pp. 3795–3797, 1995.
View at: Publisher Site | Google Scholar
H. Drexler, D. Leonard, W. Hansen, J. P. Kotthaus, and P. M. Petroff, “Spectroscopy of quantum levels in charge-tunable InGaAs quantum dots,” Physical Review Letters, vol. 73, no. 16, pp. 2252–2255, 1994.
View at: Publisher Site | Google Scholar
G. Medeiros‐Ribeiro, D. Leonard, and P. M. Petroff, “Electron and hole energy levels in InAs self‐assembled quantum dots,” Applied Physics Letters, vol. 66, no. 14, pp. 1767–1769, 1995.
View at: Publisher Site | Google Scholar
M. Narihiro, G. Yusa, Y. Nakamura, T. Noda, and H. Sakaki, “Resonant tunneling of electrons via 20 nm scale InAs quantum dot and magnetotunneling spectroscopy of its electronic states,” Applied Physics Letters, vol. 70, no. 1, pp. 105–107, 1997.
View at: Publisher Site | Google Scholar
M. Grundmann, O. Stier, and D. Bimberg, “InAs/GaAs pyramidal quantum dots: strain distribution, optical phonons, and electronic structure,” Physical Review B, vol. 52, no. 16, pp. 11969–11981, 1995.
View at: Publisher Site | Google Scholar
M. A. Cusack, P. R. Briddon, and M. Jaros, “Electronic structure of InAs/GaAs self-assembled quantum dots,” Physics Review, vol. 54, no. 4, pp. R2300–R2303, 1996, B54.
View at: Publisher Site | Google Scholar
O. Marquardt, E. P. O’Reilly, and S. Schulz, “Electronic properties of site-controlled (111)-oriented zinc-blende InGaAs/GaAs quantum dots calculated using a symmetry-adapted k⋅p Hamiltonian,” Journal of Physics: Condensed Matter, vol. 26, no. 3, article 035303, 2014.
View at: Publisher Site | Google Scholar
J. D. Plumhof, R. Trotta, V. Křápek et al., “Tuning of the valence band mixing of excitons confined in GaAs/AlGaAs quantum dots via piezoelectric-induced anisotropic strain,” Physical Review B, vol. 87, no. 7, article 075311, 2013.
View at: Publisher Site | Google Scholar
R. Poersschke and O. Madelung, Eds., Data in Science and Technology, Semiconductors, Group IV Elements and III-V Compounds, Springer-Verlag, Berlin, Germany, 1991.
I. Vurgaftman, J. R. Meyer, and L. R. Ram-Mohan, “Band parameters for III–V compound semiconductors and their alloys,” Journal of Applied Physics, vol. 89, no. 11, pp. 5815–5875, 2001.
View at: Publisher Site | Google Scholar
C. G. Van de Walle, “Band lineups and deformation potentials in the model-solid theory,” Physical Review B, vol. 39, no. 3, pp. 1871–1883, 1989.
View at: Publisher Site | Google Scholar
J. H. Neave, B. A. Joyce, P. J. Dobson, and N. Norton, “Dynamics of film growth of GaAs by MBE from Rheed observations,” Applied Physics A Solids and Surfaces, vol. 31, no. 1, pp. 1–8, 1983.
View at: Publisher Site | Google Scholar
B. A. Joyce, P. J. Dobson, J. H. Neave et al., “RHEED studies of heterojunction and quantum well formation during MBE growth — from multiple scattering to band offsets,” Surface Science, vol. 168, no. 1-3, pp. 423–438, 1986.
View at: Publisher Site | Google Scholar
M. A. Herman and H. Sitter, Molecular Beam Epitaxy, Springer-Verlag, Heidelberg, Germany, 2nd edition, 1996.
View at: Publisher Site
T. Sakamoto, H. Funabashi, K. Ohta, T. Nakagawa, N. J. Kawai, and T. Kojima, “Phase-locked epitaxy using RHEED intensity oscillation,” Japanese Journal of Applied Physics, vol. 23, 9, Part 2, pp. L657–L659, 1984.
View at: Publisher Site | Google Scholar
D. Leonard, K. Pond, and P. M. Petroff, “Critical layer thickness for self-assembled InAs islands on GaAs,” Physical Review B, vol. 50, no. 16, pp. 11687–11692, 1994.
View at: Publisher Site | Google Scholar
J. H. Davies, The Physics of Low-Dimensional Semiconductors, Cambridge University Press, Cambridge, UK, 1998.
M. O. Watanabe, J. Yoshida, M. Mashita, T. Nakanisi, and A. Hojo, “Band discontinuity for GaAs/AlGaAs heterojunction determined by C‐V profiling technique,” Journal of Applied Physics, vol. 57, no. 12, pp. 5340–5344, 1985.
View at: Publisher Site | Google Scholar
G. Bastard, Wave Mechanics Applied to Semiconductor Heterostructures, Les editions de Physique, Paris, France, 1988.
T. Saito, H. Ebe, Y. Arakawa, T. Kakitsuka, and M. Sugawara, “Optical polarization in columnar InAs/GaAs quantum dots: 8-band k⋅p calculations,” Physical Review B, vol. 77, no. 19, 2008.
View at: Publisher Site | Google Scholar
J. H. Davies, “Elastic and piezoelectric fields around a buried quantum dot: a simple picture,” Journal of Applied Physics, vol. 84, no. 3, pp. 1358–1365, 1998.
View at: Publisher Site | Google Scholar
J. H. Davies, “Quantum dots induced by strain from buried and surface stressors,” Applied Physics Letters, vol. 75, no. 26, pp. 4142–4144, 1999.
View at: Publisher Site | Google Scholar
G. E. Pikus and G. L. Bir, “Effect of deformation on the hole energy spectrum of germanium and silicon,” Soviet Physics - Solid State, vol. 1, p. 1502, 1960.
View at: Google Scholar
G. D. Mahan, Many-Particle Physics, Plenum Press, New York, NY, USA, 2nd edition, 1990.
View at: Publisher Site
G. E. Bir and G. L. Pikus, Symmetry and Strain Induced Effects in Semiconductors, Wiley, New York, NY, USA, 1974.
G. Ji, S. Agarwala, D. Huang, J. Chyi, and H. Morkoc, “Band lineup in GaAs_1−xSb_x/GaAs strained-layer multiple quantum wells grown by molecular-beam epitaxy,” Physical Review B, vol. 38, no. 15, pp. 10571–10577, 1988.
View at: Publisher Site | Google Scholar
M. Tanaka, H. Sakaki, and J. Yoshino, “Atomic-scale structures of top and bottom heterointerfaces in GaAs–Al_xGa_1-xAs (x=0.2-1) quantum wells prepared by molecular beam epitaxy with growth interruption,” Japanese Journal of Applied Physics, vol. 25, 2, Part 2, pp. L155–L158, 1986.
View at: Publisher Site | Google Scholar
R. Songmuang, S. Kiravittaya, and O. G. Schmidt, “Shape evolution of InAs quantum dots during overgrowth,” Journal of Crystal Growth, vol. 249, no. 3-4, pp. 416–421, 2003.
View at: Publisher Site | Google Scholar

Copyright

Copyright © 2019 Takuya Kawazu. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

PDF Download Citation

Download other formats

Order printed copies

Views

1670

Downloads

871

Citations