Free carrier accumulation at cubic AlGaN/GaN heterojunctions

Abstract

Cubic Al 0.3 Ga 0.7 N/GaN heterostructures were grown by plasma-assisted molecular beam epitaxy on 3C-SiC (001) substrates. A profile of the electrostatic potential across the cubic-AlGaN/GaN heterojunction was obtained using electron holography in the transmission electron microscope. The experimental potential profile indicates that the unintentionally doped layers show n-type behavior and accumulation of free electrons at the interface with a density of 5.1 Â 10 11 /cm 2 , about one order of magnitude less than in wurtzite AlGaN/GaN junctions. A combination of electron holography and cathodoluminescence measurements yields a conduction-to-valence band offset ratio of 5:1 for the cubic AlGaN/GaN interface, which also promotes the electron accumulation. Band diagram simulations show that the donor states in the AlGaN layer provide the positive charges that to a great extent balance the two-dimensional electron gas. V C 2012 American Institute of Physics. [http://dx.

Understanding band alignments in semiconductor heterostructures: Composition dependence and type-I–type-II transition of natural band offsets in nonpolar zinc-blendeAlxGa1−xN/AlyLandmann1, Rauls2, Schmidt3 2017Phys. Rev. B19060View full textAdd to dashboardCite

“…In contrast to the polar wurtzite phases, substantially less data have been reported on the composition dependence of band offsets between the nonpolar cubic polytypes. Wei et al [63] used a combination of electron holography and cathodoluminescence measurements to determine the strained band offsets in a zb-GaN/Al 0.3 Ga 0.7 N heterostructure grown on 3C-SiC substrate yielding valence and conduction band offsets of −0.13 and 0.65 eV, respectively, and a high conduction-to-valence band-offset ratio of 5:1. A smaller zb-GaN/Al 0.3 Ga 0.7 N band-offset ratio of 0.5/0.15 ≈ 3.3 was determined by Mourad [44] using branch-point alignment of empirical tight-binding band energies to determine unstrained natural band offsets.…”

Precession electron diffraction‐assisted crystal phase mapping of metastable c‐GaN films grown on (001) GaAs

“…The study of these materials has been carried out using mainly the stable phase, which has a hexagonal (wurtzite) structure with space group P63mc . However, this crystal phase presents large spontaneous and piezoelectric polarization fields that limit the free‐carrier recombination efficiency (Wei et al, ). Recently, in order to avoid the intrinsic polarization fields in electronic devices, intensive efforts have been made to grow the group III nitrides in the metastable phase, which has a cubic (zinc blende) structure with space group F‐43m (As et al, ; Casallas‐Moreno et al, ; Wei et al, ).…”

“…However, this crystal phase presents large spontaneous and piezoelectric polarization fields that limit the free‐carrier recombination efficiency (Wei et al, ). Recently, in order to avoid the intrinsic polarization fields in electronic devices, intensive efforts have been made to grow the group III nitrides in the metastable phase, which has a cubic (zinc blende) structure with space group F‐43m (As et al, ; Casallas‐Moreno et al, ; Wei et al, ). The cubic phase does not exhibits spontaneous polarization due to the high crystal symmetry, and all piezoelectric polarization components vanish along the <100> direction of growth (Sun and Towe, ), contrary to the wurtzite type where the total polarization is never zero for any orientation (Wei et al, ).…”

Mixed Phases at the Bottom Interface of Si‐Doped AlGaN Epilayers of Optoelectronic Devices

“…GaN and its alloys (e.g., AlGaN, InAlN, and InGaN) are foundations for new optoelectronic devices such as blue/violet light-emitting diode (LED), high electron mobility transistor (HEMT), ultraviolet and/or infrared photodetectors, and plasmonic Terahertz detectors [1][2][3][4][5][6][7]. GaN usually exists in either a hexagonal wurtzite (h) or a cubic zinc blende (c) structure [1,2,8,9]. Devices based on the two crystalline structures show very different optical and electrical performances.…”