Research on Degradation of GaN-Based Blue LED Caused by <i>γ</i> Radiation under Low Bias

Zhao, Qifeng; Lu, Xiangyang; Yu, Fajun; Xu, Jinglei; Fang, Zeping; Liu, Xiao-yong

doi:https://doi.org/10.1155/2020/1592695

International Journal of Optics

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Research Article | Open Access

Volume 2020 | Article ID 1592695 | https://doi.org/10.1155/2020/1592695

Research on Degradation of GaN-Based Blue LED Caused by γ Radiation under Low Bias

Qifeng Zhao,¹Xiangyang Lu,¹Fajun Yu,¹Jinglei Xu,¹Zeping Fang,¹and Xiao-yong Liu¹

Academic Editor: John T. Sheridan

Received11 Sept 2019

Revised13 Nov 2019

Accepted27 Nov 2019

Published24 Feb 2020

Abstract

GaN multiquantum-well blue light-emitting diodes (LEDs) were radiated with ⁶⁰Co γ-rays for accumulated doses up to 2.5 Mrad (SiO₂). The radiation-induced current and 1/f noise degradations were studied when the devices operate at the low bias voltage. The current increased by 2.31 times, and the 1/f noise increased by 275.69 times after a dose of 2.5 Mrad (SiO₂). Based on Hurkx’s trap-assisted tunneling model, the degradation of current was explained. γ radiation created defects in the space-charge region of LEDs. These defects as generation-recombination centers lead to the increase in the current. In addition, based on the quantum l/f noise theory, the degradation of 1/f noise might be also attributed to these defects, which caused an increase in the Hooge constant and a decrease in the carrier lifetimes. The current and 1/f noise degradations can be attributed to the same physical origin. Compared to the current, the 1/f noise parameter is more sensitive, so it may be used to evaluate the radiation resistance capability of GaN blue LEDs.

1. Introduction

With the further development of space technology and electronic technology, GaN-based light-emitting diodes (LED) as light source are more and more used in satellites, spacecrafts, missiles, and other equipments. Devices work in space affected unavoidably by the space radiation. There is strong interest in the effects of directly or indirectly ionizing radiation on GaN-based LEDs for space-based applications and radiation monitoring. It is important to study the effect of radiation on the GaN-based LED and to find the physical origin of the degradation mechanisms, having sensitive reliability indicators for its application. The radiation degradation modes in GaN LEDs have been investigated recently. A variety of radiation studies have been carried out [1–7], but there are few studies on the effects of γ radiation on them [8, 9]. Khanna et al. [8] found that forward turn-on voltage was increased slightly, the reverse breakdown voltage was unchanged, and the light output intensity was decreased after GaN-based LEDs were radiated by γ-rays. Li et al. [9] found the redshift of the photoluminescence peak energy of blue GaN-based LEDs exposed to γ-rays.

It is known that low-frequency noise characterization is a sensitive tool to investigate the device quality and to track the changes in the structures. In particular, the 1/f noise has been found suitable for study of the physical mechanisms of degradation caused by radiation. It is shown that low-frequency noise characteristic investigation is a sensitive method for explaining quality and reliability problems of optoelectronic devices (laser and LEDs and photodetectors) [10–14]. The low-frequency noise level could be an important indicator of the LED’s degradation caused by radiation. Investigation of low-frequency noise characteristics may give valuable information on the physical mechanisms of degradation of LEDs. Nevertheless, there are very few papers where the degradations of 1/f noise caused by γ radiation in LEDs are investigated.

In this paper, the degradation mechanism of 1/f noise in GaN multiquantum-well blue LEDs caused by γ radiation is studied. Often, a typical I-V curve of GaN-based LEDs can be divided into three regions when they operate at the forward bias [11, 15–22],that is, the tunneling current region, the diffusion-recombination current region, and the series resistance region. The mechanism of current and 1/f noise in these three parts is different, so the degradation mechanism after γ radiation may be different. For the sake of simplicity, it is only studied the degradation mechanism of current and noise of GaN-based blue LEDs after γ radiation under low voltage bias. It is found that defects in the space-charge region which are caused by γ radiation lead to the degradation of current and noise parameters.

2. Experiment

The experimental devices are GaN multiquantum-well blue LEDs produced by a Taiwan electronics company. GaN epitaxial layers were grown on sapphire substrates by the chemical vapor deposition (MOCVD). From bottom to top, GaN buffer layer, n-GaN layer, n-AlGaN layer, and InGaN quantum-well active region are in turn. The upper part is Mg-doped p-AlGaN layer and p-GaN layer. The devices were radiated with γ ray from a ⁶⁰Co source at room temperature. The accumulated total dose at each test step was 30 k, 60 k, 200 k, 500 k, 1 M, and 2.5 Mrad (SiO₂). The electrical parameters were measured by an HP4156 semiconductor parameter analyzer. The noise signal was amplified with a PARC113 low noise amplifier and then measured with an XD3020 noise measurement system based on virtual instrument that was described in [23].

3. Results and Discussions

3.1. Results

Because the devices are indeed radiation hard, the parameters of GaN-based blue LEDs did not change significantly when the total radiation dose to the device is much lower than 500 krad (SiO₂). The parameters of the device change obviously, when the total dose of radiation reaches 1 Mrad (SiO₂). Figure 1 shows the I-U curve of the low bias voltage. As can be seen from Figure 1, the precision of the measurement is too low (below 1.5 V) to get reliable values. Figure 1 shows that the current increases with the total dose of radiation at the same voltage. The relative change in the current, ΔI/I₀, is plotted versus the total dose in Figure 2 when the bias voltage is 2.23 V, where ΔI = I − I_0,I₀ is the preradiation parameter, and I is the postradiation parameter. Figure 2 shows that ΔI/I increases with total dose.

Figure 3shows the change in the current noise power spectral density of GaN-based blue LEDs before and after γ radiations when the current equals to 5 μA. As can be seen from Figure 3, the low-frequency noise is the 1/f noise for frequencies below 1 kHz. Figure 3 shows that the performance of the 1/f noise is degraded significantly with accumulated total dose. The relative change in the current noise power spectral density, ΔS_I/S_I0, is plotted versus the total dose in Figure 4 at 20 Hz, where ΔS_I = S_I − S_I0,S_I0 is the preradiation parameter, and S_I is the postradiation parameter. Figure 4 shows that ΔS_I/S_I0 increases with total dose.

3.2. Discussions

It has been pointed out in many literatures [11, 15–22] that the trap-assisted tunneling current is the main component of the GaN-based LED current when it is biased forward at low voltage (generally less than its turn-on voltage). Recently, it was shown that Hurkx’s trap-assisted tunneling model [24] might have been applied to GaN PN junctions [25–27]. Hurkx’s model is basically the conventional SRH recombination model with an electric-field-dependent reduction of the carrier lifetimes. The lifetime reduction is due to the fact that at high electric fields, both the carrier capture and emission rates are enhanced by virtue of phonon-assisted tunneling as illustrated in Figure 5. The SRH recombination rate of Hurkx’s model can be written as [24, 27]where U_GR is the SRH recombination rate, k is the Boltzmann constant, T is the temperature, E_t is the trap level, E_Fi is the Fermi level, n is the electron concentration, p is the hole concentration, and n_i is the intrinsic carrier concentration.

are the carrier lifetimes of electrons and holes in the absence of an electric field (where N_T is the trap density and c_n0 and _p0 are the electron and hole capture rates in the absence of an electric field). Γ_n and Γ_p are the field-effect functions, and they are expressed as [24]where K_n,_p is expressed as [24]where are the effective masses of electrons and holes for the trap-assisted tunneling. F(x) is the electrostatic field. ћ is reduced Planck constant. Functions D_n and D_p represent the size of a range of energies, from which the tunneling is possible. For electrons, it reads (compare Figure 5) [24]

Similarly, for holes we have [24]

The trap-assisted tunneling current can be written aswhere A is the area and W is the width of space-charge region.

The behavior of neutral radiation like γ rays passing through semiconductors is fundamentally different than the interaction with charged particles such as protons, electrons, or alpha particles, and the energy loss mechanisms are the photoelectric effect, Compton scattering, and pair production [8, 9]. γ radiation can lead to atomic displacements through secondary effects. These defects may be as generation-recombination centers in the space-charge region. Figure 2 shows that ΔI/I increases with total dose, and the degradation mechanisms of current can be explained as follows. With the accumulation of total dose, defects increase, which corresponds to increase N_t in formula (1). It leads to the increase of recombination rate. According to formula (6), the current increases also. Therefore, the number of defects increases with the radiation dose and then causes the recombination rate to increase, and the current increases. This can explain the experimental results in Figure 1 very well.

The spectrum for I = 5 μA has a 1/f spectral shape in the range 1 Hz < f < 1 kHz.

However, no generation-recombination noise is observed. This is because only generation-recombination centers whose energy level in a few kT near the Fermi level can contribute to the generation-recombination noise. 1/f noise in semiconductor devices includes surface noise and bulk 1/f noise. Since the GaN-based blue LEDs are indeed radiation hard, surface effects are less likely. It may be suggested that the defects introduced by the radiation cause changes in the 1/f noises. The reason for the increase in the noise is that the bulk 1/f noise changes.

In diodes operating at low temperatures, the current comes about by recombination of holes and electrons in the junction space-charge region. For forward bias, an electron and a hole are sequentially trapped by a recombination center, and for back bias, an electron and a hole are sequentially emitted by such a center. In addition, the emitted electrons and holes are accelerated in the space-charge region, and the electrons and holes coming from the n and p-regions, respectively, are decelerated in the space-charge region before being trapped. All these processes produce (quantum) 1/f noise [28, 29]. The time constants fluctuate in a 1/f fashion, and this produces the quantum l/f noise. For GaN-based blue LEDs at the low bias, the current comes about by recombination of holes and electrons in the junction space. So, 1/f noise of GaN-based blue LEDs is quantum 1/f noise. The quantum 1/f noise in the bulk space-charge region of PN can be expressed as [28, 29]where f is the frequency. 1/f noise in semiconductor devices is low-frequency noise [30]. τ_n,_p is the carrier lifetimes in the existence of the electric field. α_H is an empirical factor, the Hooge parameter, and it can be expressed as [28, 29]where a = 1/(137) is the fine structure constant and V is the bias voltage, V_d is the diffusion potential of the junction, c is the light speed, is the electron effective mass, and is the hole effective mass.

The carrier lifetime reduction is due to the fact that at electric fields both the carrier capture and emission rates are enhanced. The carrier lifetimes τ_n,_p in the existence of the electric field can be expressed as [27]

Let us calculate the experimental value a_H/(τ_n + τ_p) at I = 5 μA before radiation. Using (7) and the experiment data, we calculate a_H/(τ_n + τ_p) = 7.5 × 10². If the carrier lifetime is 10⁻⁹ s [10, 11], we calculate a_H = 7.5 × 10⁻⁷. Using (8) and taking = 0.2 m and = 1.7 m (m is the electron effective mass), we calculate a_H ≈ 4.6 × 10⁻⁹ in theory. The Hooge constant differs by two orders of magnitude in experiment and theory. If Hurkx’s model is considered, the carrier lifetime is affected by the field strength, and the lifetime is reduced. If the carrier lifetime is 10⁻¹⁰–10⁻¹¹ s [26], the Hooge constant is little different in experiment and theory.

The degradation mechanisms of 1/f noise can be explained as follows. γ radiation can cause defects in the space-charge region of GaN-based blue LEDs. These defects may be generation-recombination centers. When the current is constant, it is shown that the applied voltage decreases with the radiation total dose in Figure 1. According to (8), as the voltage decreases, the Hooge constant increases. At the same time, the electric field F in the space-charge region increases with the decrease of voltage. According to (2) and (3), the field-effect functions Γ_n,_p increase with the electric field F. According to (9), the carrier lifetimes τ_n,_p decrease with the increase of Γ_n,_p. In addition, the increase of defects caused by γ radiation can reduce carrier lifetime also. So, the Hooge constant α_H increases and the carrier lifetimes τ_n,_p decrease after γ radiation when the current I is constant. According to (7), after γ radiation, the conclusion can be drawn that the noise power spectral density S_I increases with the total dose of radiation when the current is constant.

The current and 1/f noise degradation of GaN-based blue LEDs attributed to the same physical origins which are the defects caused by γ radiation. So, the 1/f noise may be used as a means to evaluate the degradation of GaN-based blue LEDs which is caused by γ radiation. In order to make a comparison, ΔI/I₀ and ΔS_I/S_I0 are plotted versus the total dose in Figure 6. It shows that their degradations have a similar trend, and the increase in the 1/f noise is more significant than in the current on the same total dose. After a radiation dose up to 2.5 Mrad (SiO₂), ΔI/I₀ is 3.16 and ΔS_I/S_I0 is 275.69. It is clear that the ΔS_I/S_I0 is more sensitive than ΔI/I₀.

4. Conclusions

The radiations cause defects in the space-charge region of LEDs, which leads to the variance of current and the 1/f noise when the devices operate at the low bias voltage. These defects as generation-recombination centers lead to the increase of recombination rate, which leads to the increase of trap-assisted tunneling. In addition, these defects can cause an increase in the Hooge constant and a decrease in the carrier lifetimes, which leads to the degradation of 1/f noise. Compared to the electrical parameter, the 1/f noise parameter is more sensitive. On the basis of the research, 1/f noise measurement may be used as a means to evaluate the radiation resistance capability of GaN-based blue LEDs.

Data Availability

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

Conflicts of Interest

The authors declare that they have no conflicts of interest.

Acknowledgments

This work was supported by the Key Science and Technology Program of Henan Province, China (Grant no. 172102210589), and the Scientific Research Foundation of the Education Department of Henan Province, China (Grant no. 18B510020).

References

R. Khanna, K. K. Allums, C. R. Abernathy et al., “Effects of high-dose 40°MeV proton irradiation on the electroluminescent and electrical performance of InGaN light-emitting diodes,” Applied Physics Letters, vol. 85, no. 15, 2004.
View at: Publisher Site | Google Scholar
A. Floriduz and J. D. Devine, “Modelling of proton irradiated GaN-based high-power white light-emitting diodes,” Japanese Journal of Applied Physics, vol. 57, no. 8, Article ID 080304, 2018.
View at: Publisher Site | Google Scholar
G. Yang, Y. Jung, B.-J. Kim, and J. Kim, “Electrical and optical damage to GaN-based light-emitting diodes by 20-MeV proton irradiation,” Science of Advanced Materials, vol. 8, no. 1, pp. 160–163, 2016.
View at: Publisher Site | Google Scholar
B. J. Kim, Y. H. Hwang, S. Ahn et al., “Effects of 340°keV proton irradiation on InGaN/GaN blue light-emitting diodes,” Journal of Vacuum Science & Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phenomena, vol. 33, no. 5, Article ID 051215, 2015.
View at: Publisher Site | Google Scholar
I.-H. Lee, A. Y. Polyakov, N. B. Smirnov et al., “Point defects controlling non-radiative recombination in GaN blue light emitting diodes: insights from radiation damage experiments,” Journal of Applied Physics, vol. 122, no. 11, Article ID 115704, 2017.
View at: Publisher Site | Google Scholar
S. J. Pearton, R. Deist, F. Ren et al., “Review of radiation damage in GaN-based materials and devices,” Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 31, no. 5, Article ID 050801, 2013.
View at: Publisher Site | Google Scholar
S. J. Pearton, F. Ren, E. Patrick, M. E. Law, and A. Y. Polyakov, “Review-ionizing radiation damage effects on GaN devices,” ECS Journal of Solid State Science and Technology, vol. 5, no. 2, pp. Q35–Q60, 2016.
View at: Publisher Site | Google Scholar
R. Khanna, S. Y. Han, S. J. Pearton, D. Schoenfeld, W. V. Schoenfeld, and F. Ren, “High dose Co-60 gamma irradiation of InGaN quantum well light-emitting diodes,” Applied Physics Letters, vol. 87, no. 21, Article ID 212107, 2005.
View at: Publisher Site | Google Scholar
Y. L. Li, X. J. Wang, S. M. He et al., “Origin of the redshift of the luminescence peak in InGaN light-emitting diodes exposed to Co-60 γ-ray irradiation,” Journal of Applied Physics, vol. 112, no. 12, Article ID 123515, 2012.
View at: Publisher Site | Google Scholar
S. L. Rumyantsev, S. Sawyer, M. S. Shur et al., “Low-frequency noise of GaN-based ultraviolet light-emitting diodes,” Journal of Applied Physics, vol. 97, no. 12, Article ID 123107, 2005.
View at: Publisher Site | Google Scholar
S. Bychikhin, D. Pogany, L. K. J. Vandamme, G. Meneghesso, and E. Zanoni, “Low-frequency noise sources in as-prepared and aged GaN-based light-emitting diodes,” Journal of Applied Physics, vol. 97, no. 12, Article ID 123714, 2005.
View at: Publisher Site | Google Scholar
S. Pralgauskaitė, V. Palenskis, J. Matukas et al., “Reliability investigation of light-emitting diodes via low frequency noise characteristics,” Microelectronics Reliability, vol. 55, no. 1, pp. 52–61, 2015.
View at: Publisher Site | Google Scholar
H. Lischka, H. Henschel, O. Kohn et al., “Radiation effects in light emitting diodes, laser diodes, photodiodes, and optocouplers,” in Proceedings of the Second European Conference on Radiation and its Effects on Components and Systems (Cat. No. 93TH0616-3), pp. 226–231, IEEE, Saint Malo, France, September 1993.
View at: Publisher Site | Google Scholar
D. V. Kuksenkov, H. Temkin, A. Osinsky, R. Gaska, and M. A. Khan, “Low-frequency noise and performance of GaN p-n junction photodetectors,” Journal of Applied Physics, vol. 83, no. 4, pp. 2142–2146, 1998.
View at: Publisher Site | Google Scholar
L. Dobrzanski, “Low-frequency noise and charge transport in light-emitting diodes with quantum dots,” Journal of Applied Physics, vol. 96, no. 8, pp. 4135–4142, 2004.
View at: Publisher Site | Google Scholar
S. Sawyer, S. L. Rumyantsev, M. S. Shur et al., “Current and optical noise of GaN∕AlGaN light emitting diodes,” Journal of Applied Physics, vol. 100, no. 3, Article ID 034504, 2006.
View at: Publisher Site | Google Scholar
N. I. Bochkareva, A. M. Ivanov, A. V. Klochkov et al., “Hopping transport in the space-charge region of p-n structures with InGaN/GaN QWs as a source of excess 1/f noise and efficiency droop in LEDs,” Semiconductors, vol. 49, no. 6, pp. 827–835, 2015.
View at: Publisher Site | Google Scholar
M. Binder, B. Galler, M. Furitsch et al., “Investigations on correlation between I-V characteristic and internal quantum efficiency of blue (AlGaIn) N light-emitting diodes,” Applied Physics Letters, vol. 103, no. 22, Article ID 221110, 2013.
View at: Publisher Site | Google Scholar
X. A. Cao, S. F. LeBoeuf, K. H. Kim et al., “Investigation of radiative tunneling in GaN/InGaN single quantum well light-emitting diodes,” Solid-State Electronics, vol. 46, no. 12, pp. 2291–2294, 2002.
View at: Publisher Site | Google Scholar
X. A. Cao, E. B. Stokes, P. M. Sandvik, S. F. LeBoeuf, J. Kretchmer, and D. Walker, “Diffusion and tunneling currents in GaN/InGaN multiple quantum well light-emitting diodes,” IEEE Electron Device Letters, vol. 23, no. 9, pp. 535–537, 2002.
View at: Publisher Site | Google Scholar
X. A. Cao, J. M. Teetsov, M. P. D’Evelyn, D. W. Merfeld, and C. H. Yan, “Electrical characteristics of InGaN∕GaN light-emitting diodes grown on GaN and sapphire substrates,” Applied Physics Letters, vol. 85, no. 1, pp. 7–9, 2004.
View at: Publisher Site | Google Scholar
L. Liu, M. Ling, J. Yang et al., “Efficiency degradation behaviors of current/thermal co-stressed GaN-based blue light emitting diodes with vertical-structure,” Journal of Applied Physics, vol. 111, no. 9, Article ID 093110, 2012.
View at: Publisher Site | Google Scholar
J. L. Bao, Y. Q. Zhuang, L. Du et al., “Noise testing and analyzing system of electronic device based on virtual instrumentation,” Chinese Journal of Scientific Instrument, vol. 25, no. 4, pp. 335–356, 2004.
View at: Google Scholar
G. A. M. Hurkx, D. B. M. Klaassen, and M. P. G. Knuvers, “A new recombination model for device simulation including tunneling,” IEEE Transactions on Electron Devices, vol. 39, no. 2, pp. 331–338, 1992.
View at: Publisher Site | Google Scholar
M. Auf der Maur, B. Galler, I. Pietzonka, M. Strassburg, H. Lugauer, and A. Di Carlo, “Trap-assisted tunneling in InGaN/GaN single-quantum-well light-emitting diodes,” Applied Physics Letters, vol. 105, no. 13, Article ID 133504, 2014.
View at: Publisher Site | Google Scholar
K. Sakowski, L. Marcinkowski, S. Krukowski, S. Grzanka, and E. Litwin-Staszewska, “Simulation of trap-assisted tunneling effect on characteristics of gallium nitride diodes,” Journal of Applied Physics, vol. 111, no. 12, Article ID 123115, 2012.
View at: Publisher Site | Google Scholar
M. Mandurrino, M. Goano, M. Vallone et al., “Semiclassical simulation of trap-assisted tunneling in GaN-based light-emitting diodes,” Journal of Computational Electronics, vol. 14, no. 2, pp. 444–455, 2015.
View at: Publisher Site | Google Scholar
A. Van der Ziel and P. H. Handel, “1/f noise in n⁺-p diodes,” IEEE Transactions on Electron Devices, vol. 32, no. 9, pp. 1802–1805, 1985.
View at: Publisher Site | Google Scholar
A. Van der Ziel, P. H. Handel, X. L. Wu, and J. B. Anderson, “Review of the status of quantum 1/f noise in n⁺-p HgCdTe photodetectors and other devices,” Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 4, no. 4, pp. 2205–2216, 1986.
View at: Publisher Site | Google Scholar
K. L. Schick and A. A. Verveen, “1/f noise with a low frequency white noise limit,” Nature, vol. 251, no. 5476, pp. 599–601, 1974.
View at: Publisher Site | Google Scholar

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Copyright © 2020 Qifeng Zhao et al. 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.

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