Abstract Body: The use of p-type superlattices (SL) is valuable for III-nitride semiconductor-based LEDs and pFETs (p-type Field effect transistors) because the polarization effects create a periodic oscillation of the energy bands, enhancing the ionization of the deep acceptors (Ex: Mg) [1-3]. Recently, the existence of acceptor traps 0.8eV above the valence band of GaN, located at the positive polarization interfaces in III-nitride systems, was shown [4]. This acceptor trap level was the main source of holes in systems which had insufficient or no Mg doping in them. The present study experimentally demonstrates the effect of these acceptor traps on the charge and mobility of holes in N-polar p-type GaN/(AlN/AlGaN) superlattices. N-polar modulation doped GaN/(AlN/Al0.24Ga0.75N) 7-period superlattices were grown using metalorganic chemical vapor deposition (MOCVD). Each superlattice period was 20nm thick composed of 5nm GaN:Mg /5nm unintentionally doped (u.i.d) GaN/ x nm u.i.d. AlN/ (5-x) nm u.i.d AlGaN/ 5nm AlGaN:Mg, where the AlN layer thickness, x, was 0 nm ≤ x ≤ 1.6 nm. In addition to the AlN thickness series, the Mg doping was varied for each AlN thickness with 3.75×1018 cm-3 ≤ [Mg]≤ 2.5×1019 cm-3. The Mg doping in the samples was calibrated using Secondary Ion Mass Spectroscopy, and the SL quality and composition was measured using X-Ray Diffraction. Mg activation was carried out at 800○C and Pd/Au contacts were deposited to prepare the samples for room temperature Hall measurements. The experimental results were compared to those calculated using STR-FETIS. When the band-bending of both GaN and AlN was < 0.8eV, the sheet charge concentration of holes (ps) measured using Hall matched with the calculated values. For each of the samples where band-bending of either GaN or AlN was ≥ 0.8eV(without accounting for the impact of trap ionization on band-bending), the measured ps was greater than the amount of Mg dopants put into the sample. This showed that the excess holes came from the acceptor traps at the positive polarization interfaces, here - AlGaN/GaN and AlN/AlGaN interfaces. The acceptor trap ionized when either band-bending was ≥ 0.8eV and the Fermi level was pinned at this trap level leading to the very high measured ps. A low sheet resistance (~3.4kΩ/■) was observed for N-polar modulation doped GaN/AlN/AlGaN SLs, with ps~1.3×1014 cm-2 and µp~14 cm2/Vs. For the samples in this study, the two-dimensional hole gas (2DHG) exists at the GaN/AlN interface or a GaN/AlGaN interface, if no AlN present. It was observed for each of the AlN thickness series (with various Mg doping levels) the µp decreased in samples where the acceptor traps ionized. It was further observed within those set of samples that µp decreased to a great extent (>50% decrease) for those samples where AlN band-bending was ≥ 0.8eV – independent of the GaN band-bending in the same sample. The 2DHG is closer to the AlN/AlGaN positive polarization interface (PPI-1) (0 to 1.6nm) compared to the AlGaN/GaN positive polarization interface (PPI-2)(10nm). Therefore, the more dominant source of scattering (and hence the decreased mobility) are the ionized acceptor traps which exist at the AlN/AlGaN positive polarization interface, the closer interface. While the ionized traps at AlGaN/GaN interface also cause scattering, their effect is not as pronounced because they are far away from the 2DHG. This explains the higher mobility observed in in samples where only the GaN band-bending was ≥ 0.8eV, and the AlN band-bending was < 0.8eV leading to the ionization of traps at only the AlGaN/GaN positive polarization interface (PPI-2). Further details of simulations, experiments and methodology will be presented at the conference. [1] P. Kozodoy, et al., APL(1999) [2] A. Raj, et. al., IEEE-EDL (2020) [3] C.J. Zollner, et. al., OME (2020) [4] A. Krishna, et. al., APL (2020)

Effect of Acceptor Traps at Positive Polarization Interfaces on the Charge and Mobility of Holes in N-Polar P-Type GaN/(AlN/AlGaN) Superlattices

T: High Electron Mobility Transistors (HEMT) & Characterization of 2-Dimensional Electron, Hole Gases

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Effect of Acceptor Traps at Positive Polarization Interfaces on the Charge and Mobility of Holes in N-Polar P-Type GaN/(AlN/AlGaN) Superlattices

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