Electric Fields and Surface Fermi Level in Undoped GaN/AlN Two‐Dimensional Hole Gas Heterostructures

Abstract

Undoped GaN/AlN heterostructures with a high‐density 2D hole gas (2DHG) have recently been reported, demonstrating that holes can be generated in GaN without magnesium (Mg) doping. The presence of the high‐density 2DHG in these GaN/AlN heterostructures is expected to result from huge internal polarization fields. Herein, modulation spectroscopy is applied to analyze the built‐in electric fields in the top GaN layer of molecular beam epitaxy (MBE)‐grown GaN/AlN heterostructures with a buried 2DHG using contactless electroreflectance (CER). Experimentally obtained electric field values are compared with self‐consistent Schrödinger–Poisson energy band calculations of the GaN/AlN structures. This coupled experimental and theoretical analysis determines that the Fermi level at the GaN surface is located at ≈1.9 above the valence band (i.e., roughly in the middle of the bandgap)—for structures with undoped and Mg‐doped GaN. Finally, the comparison of calculated 2DHG concentrations in the structures under study with values determined from Hall effect measurements shows excellent agreement further strengthening the result.

Perovskite/GaN-Based Light-Modulated Bipolar Junction Transistor for High Comprehensive Performance Visible-Blind Ultraviolet Photodetection

“…The energy diagrams of MAPbCl 3 and GaN films in isolated status are shown in Figure S7d, which are determined by ultraviolet photoelectron spectroscopy (UPS) as shown in Figure S7a,b, with the optical band gaps derived from the Tauc plots in Figure S7c. The evaluated conduction band, valence band, and Fermi level of MAPbCl 3 and GaN are consistent with the previous studies. ,, It is observed that MAPbCl 3 /GaN forms a type II heterojunction with a well-aligned conduction band, which can be further verified by the steady-state photoluminescence (PL) spectra analysis. Figure b compares the PL spectra of GaN and MAPbCl 3 /GaN films optically pumped on the GaN layer.…”

“…The evaluated conduction band, valence band, and Fermi level of MAPbCl 3 and GaN are consistent with the previous studies. 19,33,34 It is observed that MAPbCl 3 /GaN forms a type II heterojunction with a well-aligned conduction band, which can be further verified by the steady-state photoluminescence (PL) spectra analysis. Figure 2b compares the PL spectra of GaN and MAPbCl 3 /GaN films optically pumped on the GaN layer.…”

MOVPE-grown GaN/AlGaN heterostructures on sapphire with polarization-induced two-dimensional hole gases

“…In addition, we simulated the same structure without p-GaN layer (red lines) corresponding to the etched structure and finally a reference structure with the same total GaN thickness (yet no Mg doping, orange lines). For the simulations, the surface potential was set to ϕ S = 1.6 eV, as reported for p-doped GaN grown by MOVPE [46]. Note: The surface potential values will be strongly dependent on growth conditions and preparation.…”

Depletion- and Enhancement-Mode p-Channel MISHFET Based on GaN/AlGaN Single Heterostructures on Sapphire Substrates

“…Taking the nominal etch rate and thicknesses into account, we expect sample ED4 to have been etched such that an ultra-thin p-GaN layer is left on top of the GaN, whereas sample ED5 is expected to be recessed slightly into the uid-GaN channel To form the MISHFET gate dielectric, 10 nm Al2O3 were grown by plasma-enhanced atomic layer deposition (PEALD). Al2O3 also serves as a surface passivation in the access regions [38]. The PEALD process was performed at a substrate temperature of 300 °C, and oxygen and trimethylaluminum were used as precursors.…”