Conductive layer near the GaN/sapphire interface and its effect on electron transport in unintentionally doped n-type GaN epilayers

Abstract

Temperature-dependent Hall effect measurements on unintentionally doped n-type GaN epilayers show that, above room temperature, the Hall-mobility values of different samples vary parallel with each other with temperature. We demonstrate that this anomaly is mainly due to a conductive layer near the GaN/sapphire interface for thin samples with low carrier density. Through trapping electrons, threading edge dislocations (TEDs) debilitate the epilayer contribution in a two-layer mixed conduction model involving the epilayer and the near-interface layer. The trapping may, in part, explain low mobility and anomalous transport in pure GaN layers. Scattering by TEDs is important only at low temperatures.

Defect evolution and accompanied change of electrical properties during the GaN growth by metalorganic chemical vapor deposition

“…However, the interfacelayer effects become much weaker for the Si-doped GaN epilayers which have higher conductivity. It is reported that no interfacelayer effects are observed when the carrier density of epitaxial film is above ∼4 × 10 17 cm −3 [18]. In our case, the investigated samples A-F are all Si-doped and have higher carrier concentration than undoped GaN.…”

“…3, the carrier concentration of GaN samples decrease with the increase of growth time. The carrier concentrations are 9.1 × 10 17 , It has been reported that during the initial stage of GaN growth a thin interface layer is present near the sapphire interface, which may result in a conducting channel there [18]. It is expected that this may have an important effect on the Hall measurements, especially when the GaN films are thin enough.…”

Correlation of in-situ reflectance spectra and resistivity of GaN/Al2O3 interfacial layer in metalorganic chemical vapor deposition

“…[1][2][3][8][9][10] Some research groups reported that the conductivity is presumably due to doping by residual oxygen impurities. 3,9 Others reported that the dislocations in GaN are presumably electrically active.…”

“…Because of the large lattice and thermal mismatch between GaN and sapphire, there is a highly defective layer near the GaN/ sapphire interface, which typically exhibits n-type conductivity. [1][2][3] It is still a challenge to control the resistivity of this interfacial layer in undoped GaN buffers grown on sapphire using the metal-organic chemical vapor deposition (MOCVD) technique. The properties of this interfacial layer and its influences on the material and device grown on it are not clear.…”

A new growth method of semi-insulating GaN layer for HEMT structure by eliminating degenerate layer at GaN/sapphire interface

“…It is well known that when oxygen is incorporated in GaN layer, oxygen in N-site (O N ), a source of shallow donors with activation energy of 33.2 meV in GaN, is stable [22]. O N is difficult to be formed in other regions of the film away from the interface because of limited diffusion, resulting in the limited thickness of the high oxygen concentration, generating a highly conducting channel near the sapphire substrate [23].…”