Carrier localization in III-nitride versus conventional III-V semiconductors: A study on the effects of alloy disorder using landscape theory and the Schrödinger equation

Semiconductor devices often require band-gap engineering, which in turn requires the use of alloys and the tuning of their composition to achieve the required electrical or optical behavior. While their compositional fluctuations are generally treated as a perturbation in most conventional III-V semiconductors, the effects of alloy disorder are much more significant in the III-nitrides. Here, the effects of alloy disorder on carrier localization are compared for different III-V semiconductors, particularly for holes for which localization effects are more significant due to their heavier effective mass. This study is conducted using three-dimensional computation for III-V alloys with natural (random) compositional fluctuations. Given the complexity of the problem, we carry out the computations relying on a simplified Hamiltonian in the envelope wave-function approximation with a single heavy-hole valence band. We investigate the effects of compositional fluctuations on carrier localization using two methods. The first method, based on the localization landscape theory, is used to solve the localization landscape equations and obtain the effective potentials acting on carriers. This potential acts as a confining potential that predicts the regions of spatial localization of carriers, and thus allows a comparison of the effects of alloy fluctuations between the conventional III-V and the III-nitride semiconductors. We find that the effective potential of the III-nitride semiconductors exhibits much larger fluctuations compared to the other III-V semiconductors. This might point to a higher degree of carrier localization in the nitrides, particularly for holes. This is verified through the second method, solving Schrödinger's equation and obtaining the electron and hole wave functions. We find that for InxGa1-xN the electron wave functions are delocalized even for the ground state, whereas the low-energy hole states are localized. This is in contrast with the behavior of holes in the common alloy InxGa1-xAs, which are found to be always delocalized. Thus, our study shows the importance of accounting for alloy disorder in the nitrides.