Scattering Analysis of AlGaN/AlN/GaN Heterostructures with Fe-Doped GaN Buffer

Abstract

The results of the study of the influence of Fe segregation into the unintentionally doped GaN channel layer in AlGaN/AlN/GaN heterostructures with Fe-doped GaN buffer layer on the electrical properties of two-dimensional electron gas are presented. A set of several samples was grown by metal-organic vapor-phase epitaxy and characterized by the van der Pauw method. The dependence of concentration and mobility of the two-dimensional electron gas on the channel layer thickness was analyzed theoretically by self-consistent solving of 1D Poisson and Schrödinger equations and scattering rate calculations within the momentum relaxation time approximation. It was found that both concentration and mobility decreases were responsible for the increase in the sheet resistance in the structures with a thinner channel layer, with a drop in mobility being not only due to ionized impurity scattering, but also due to a combined effect of weakening of screening, lower carrier energy and change in form-factors on scattering by interface roughness, dislocations and polar optical phonons.

Crack-Free High-Composition (>35%) Thick-Barrier (>30 nm) AlGaN/AlN/GaN High-Electron-Mobility Transistor on Sapphire with Low Sheet Resistance (<250 Ω/□)

“…Also, an increase in the thickness of the UID-GaN layer (t 1 ) in sample 3 from 200 nm to 1000 nm showed a reduction in the pinch-off voltage by −1.35 V, indicating an increase in the 2DEG charge density. The increase in the 2DEG charge is associated with a reduction in the unintentional incorporation of acceptor-type Fe dopants in the UID-GaN channel from the Fe-doped GaN buffer layer [39]. The pinch-off voltage further decreased to −8.85 V (sample 4) from −6.65 V (sample 3) when the AlGaN barrier thickness was increased from 21 nm to 31 nm, indicating an enhancement in the 2DEG charge density.…”

“…The increase in the 2DEG charge is associated with a reduction in the unintentional incorporation of acceptor-type Fe dopants in the UID-GaN channel from the Fe-doped GaN buffer layer [39]. The pinch-off voltage further decreased to −8.85 V (sample 4) from −6.65 V (sample 3) when the AlGaN barrier thickness was increased from 21 nm to 31 nm, indicating an enhancement in the 2DEG charge density.…”

“…If the 2DEG channel is in close proximity to the Fe-doped semi-insulating layer, then the electron transport might be affected due to the bulk-trapping phenomenon [36][37][38]. Dmitri S. Arteev et al have also reported the effect of UID-GaN buffer or channel layer thickness on the properties of 2DEG charge and mobility in an AlGaN/AlN/GaN HEMT with a Fe-doped GaN buffer [39]. An increased AlGaN thickness (t 3 ) from 21 nm to 31 nm in sample 4 compared to sample 3 increased the sheet charge from 1.33 × 10 13 /cm 2 (sample 3) to 1.46 × 10 13 /cm 2 due to a reduction in surface depletion, while the mobility reduced from 1800 cm 2 /V•s to 1710 cm 2 /V•s compared to sample 3.…”

AlGaN HEMT Structures Grown on Miscut Si(111) Wafers

“…All other symbols have their conventional meanings. A detailed description of the models used can be found in our previous works [ 49 , 50 ] and references therein. To keep the process simple, a single parameter set (including , which served as a fitting parameter) was used, and only an RMS roughness parameter was varied during the calculation of interface roughness scattering rate, so .…”