Electron accumulation and distribution at interfaces of hexagonal ScxAl1-xN/GaN- and ScxAl1-xN/InN-heterostructures

摘要

Electron charges and distribution profiles induced by polarization gradients at the interfaces of pseudomorphic, hexagonal ScxAl1-xN/GaN- and ScxAl1-xN/InN-heterostructures are simulated by using a Schrodinger-Poisson solver across the entire range of random and metal-face ScxAl1-xN-alloys, considering the transition from wurtzite to hexagonal layered crystal structure. In contrast to previous calculations of polarization-induced sheet charges, we use Dryer's modern theory of polarization, which allows for consideration of the spontaneous polarization measured on ferroelectric ScxAl1-xN-layers. Because the sheet density of the electrons accumulating at the heterostructure interfaces can strongly depend both on the data set of the piezoelectric and structural coefficients and on the alloying region of the ScxAl1-xN-layers in which the transition from the wurtzite to the hexagonal layered crystal structure occurs, we have calculated the charge carrier sheet densities and profiles for three representative data sets and evaluated their relevance for devices. We predict electron sheet densities of ( 2.26 +/- 0.20 ) x 10 14 c m - 2 and ( 6.25 +/- 0.20 ) x 10(14) cm(-2) for all three sets of data for Ni/AlN/InN- and Ni/ScN/InN-heterostructures, respectively. We demonstrate that the polarization-induced interface charges of Ni/ScxAl1-xN/InN-heterostructures are always positive, tend to increase with increasing Sc-content, and can cause electron accumulations that lead to flooding of the triangular quantum wells at the semiconductor interface. We identify Ni/ScxAl1-xN/GaN-heterostructures with 0.13 <= x <= 0.19 as particularly promising candidates for the processing of energy-efficient high electron mobility transistors due to their missing or low mechanical strain and their large electron sheet densities between ( 4.11 +/- 0.20 ) x 10 (13) cm(-2) and ( 6.37 +/- 0.20 ) x 10(13) c m(-2). Furthermore, we present simulation results of highly strained Ni/ScxAl1-xN/GaN-heterostructures for 0.81 <= x <= 1.0, which point to electron accumulations of up to ( 8.02 +/- 0.40 ) x 10(14) c m(-2) . These heterostructures are not suitable for transistor devices, but they may be of great interest for the implementation of low impedance contacts.