Two-dimensional electron gas at the AlGaN/GaN interface: Layer thickness dependence

Abstract

In the current paper, the structure and properties of AlGaN/GaN interfaces are studied, explaining the role of AlGaN layer thickness on the two-dimensional electron gas (2DEG) formation. It is found that the generation of a continuous electron gas requires AlGaN films with stable stoichiometry, which can be reached only above a certain critical thickness, ≈6-7 nm in our case (20 at. % Al content). Thinner films are significantly affected by oxidation, which causes composition variations and structural imperfections leading to an inhomogeneity of the polarization field and, as a consequence, of the electron density across the interface. Using Kelvin probe force microscopy, this inhomogeneity can be visualized as variations of the surface potential on the sub-micrometer scale. For heterostructures with layer thickness above the critical value, the surface potential maps become homogeneous, reflecting a weakening influence of the oxidation on the interface electronic properties. The 2DEG formation is confirmed by the Hall measurements for these heterostructures.

HADOKEN: An open-source software package for predicting electron confinement effects in various nanowire geometries and configurations

“…In GaN/AlGaN heterostructures, a spatially-dependent polarization, P(r), arises from two sources: (1) the spontaneous polarization, P s , due to the difference in electronegativities between GaN/AlGaN that leads to the formation of molecular dipole fields [28], and (2) the piezoelectric polarization, P p , due to the lattice mismatch at the epitaxially grown GaN/AlGaN interface that induces strain during thermal expansion. In both cases, a non-zero charge density emerges at the GaN/AlGaN interface due to the discontinuity in P = P s + P p .…”

Power Electronics Based on Wide-Bandgap Semiconductors: Opportunities and Challenges

“…Beyond the effort in improving channel mobility, today one can choose devices in which transport occurs in the bulk, such as JFETs [21], [22]. GaN, instead, has an advantage in terms of the achievable 2D mobility [23], due to a very high density of the 2D electron gas at the GaN/AlGaN interface, and modulation doping using AlGaN piezoelectric properties [24].…”

Understanding the onset of negative electronic compressibility in one- and two-band 2D electron gases: Application to LaAlO$_3$/SrTiO$_3$

“…Highly tunable electron-electron interactions at interfaces have been shown to host states with charge, spin, and orbital orderings [3][4][5][6][7][8] that emerge from the two-dimensional electron gas (2DEG) at the interface. [9][10][11][12][13][14] While there are many interesting properties of the 2DEG, we focus on the observations of negative electronic compressibility (NEC). NEC is produced through electron-electron interactions, where the exchange and Coulomb energies outweigh the overall kinetic energy of the electronic system [15][16][17][18][19].…”