Formation mechanism of a degenerate thin layer at the interface of a GaN/sapphire system

Abstract

It has recently been suggested that the thin degenerate layer found at the GaN/sapphire interface results from a high concentration of stacking faults. The studies of this letter, however, show that this is not the most likely explanation for the presence of such a degenerate layer. Using x-ray energy-dispersive spectroscopy and secondary ion-mass spectroscopy, profile distributions of elements Ga, N, O, C, and Al, near the interface, have been obtained. The distributions reveal very high O and Al concentrations in the GaN film within 0.2 m from the interface, together with a material depletion of Ga and N. Such conditions strongly favor n ϩ conductivity in this interfacial region because not only are N-vacancy and N-site O donors present, but Al incorporated on the Ga sublattice reduces the concentration of compensating Ga-vacancy acceptors. The two-layer ͑film plus interface͒ conduction has been modeled, and the effect of conduction in the GaN film thus isolated.

Impurity band in the interfacial region of GaN films grown by hydride vapor phase epitaxy

“…Similar increases in O concentration near the interface were reported for GaN films grown by MBE 20 and MOCVD. 21 The most likely source of oxygen is the sapphire substrate, from which oxygen diffuses into the GaN at the high growth temperature. This is also consistent with the larger interfacial layer thickness found in thicker GaN films (Fig.…”

Depth-dependent investigation of defects and impurity doping in GaN/sapphire using scanning electron microscopy and cathodoluminescence spectroscopy

“…Hence, impurity diffusion, interface reaction, and related defect formation are important to understand and control. The physical origin of the donors has until now been unclear since it may involve: ͑i͒ impurities substrate out-diffusion [11][12][13] or the initial growth surface, ͑ii͒ native defects induced by substrate out-diffusion or the initial growth surface, ͑iii͒ morphological structural effects, and ͑iv͒ gas phase impurities. In order to determine the physical nature of these dopants and defects, we used temperature-dependent ͑10-300 K͒ electron-excited luminescence spectroscopy in an ultrahigh vacuum ͑UHV͒ scanning electron microscope ͑SEM͒ to measure defect emissions from GaN/Al 2 O 3 junctions with sheet carrier densities that varied over two orders of magnitude.…”

Microcathodoluminescence of impurity doping at gallium nitride/sapphire interfaces

“…In particular, near the GaN interface with sapphire, the most common growth substrate for device development, degenerate doping, and high conductance 1,2 degrade the control of the transport in the overall epilayer. The physical origin of the donors may involve: ͑i͒ native defects, impurities, or complexes generated from the substrate [3][4][5] or the initial growth surface; or ͑ii͒ morphological defects such as dislocations or stacking faults. In order to determine the physical nature of these donors, we used low temperature ͑10 K͒ electron-excited luminescence spectroscopy in an ultrahigh vacuum ͑UHV͒ scanning electron microscope ͑SEM͒ to measure defect emissions from GaN/Al 2 O 3 junctions with sheet carrier densities that varied over two orders of magnitude.…”