Physics of Internal Photoemission and Its Infrared Applications in the Low-Energy Limit

Figure 8

(a) The valence band diagram of a graded (solid line)/flat (dashed line) barrier structure. Bidirectional photocurrents can simultaneously exist in the sample for photovoltaic operation, as shown by (+) and (−), corresponding to forward and reverse photocurrents, respectively. , , and are the Al fractions of the barriers as described in Table 2. is an offset between the barriers below and above the emitter. (b) Schematic of optical transitions between two valence bands, that is, the heavy-hole (hh) and light-hole (lh) bands. For holes to escape over a potential barrier, optical transitions typically occur with the assistance of phonons.

(a)

(b)