Unintentional doping of a-plane GaN by insertion of in situ SiN masks

Abstract

Undoped a-plane GaN layers grown by metal organic vapor phase epitaxy on sapphire (10-12) substrates using low temperature GaN seed layers and in-situ SiN masks were characterized by Hall-effect measurements, CV-characteristics and photovoltage spectroscopy. With increasing deposition time of the SiN masks the electron concentrations of the GaN layers are enhanced. The dominant activation energy between 14 meV and 22 meV determined by temperature dependent Hall-effect is very similar to the donor silicon on gallium site. Two other activation energies at 30 meV and between 50 meV and 70 meV were found corresponding well with O Ga and V N defects, respectively. The depth profiles of the net donor densities show a strong increase towards the substrate /LT-GaN/HT-GaN interface indicating diffusion of silicon from the SiN mask towards the surface. Therefore, the Si-doping is attributed to the dissolution of the SiN masks during the following high temperature GaN layer growth. Sidoping from the SiN masks also explains the deterioration of the band bending within the LT-GaN / HT-GaN junction found by photovoltage spectroscopy.

Improving GaN‐on‐silicon properties for GaN device epitaxy

“…Typical is an in-situ deposited SiN masking layer, however recently a BN layer has been reported to be also suited for this purpose [29]. In-situ deposited SiN, usually with a thickness around a monolayer, does always act as n-type dopand in GaN, either by diffusion into the growing GaN layer, or at least when it is directly neighbouring to GaN where the Si atoms act as donors and form a delta doped layer [30]. This can typically be observed as doping or conductivity contrast in SEM measurements but also in Hall-effect or C-V measurements of a nominally undoped GaN layer.…”

Structural and electrical anisotropies of Si-doped a-plane (11–20) GaN films with different SiNx interlayers

“…In this study, however, the increased carrier concentration in samples with a SiN x interlayer is most likely due to Si Ga because a high concentration of oxygen exists in a region near the GaN/sapphire interface. A recent study demonstrated diffusion of Si from SiN x nanomasks, which resulted from dissolution of the nanomasks during the subsequent HT-GaN growth, as an unintended Si doping source in an a-plane GaN film [34]. Hence, in this study, subsequent GaN growth at the high temperature and high flow rates of SiH 4 used in SiN x layer deposition increase the carrier concentration in the a-plane GaN samples containing a SiN x layer (B, C and D), as is evident from the data given in table 1.…”