Li Peixian

Stress and morphology of a nonpolar a -plane GaN layer on r -plane sapphire substrate

The anisotropic strain of a nonpolar (110) a-plane GaN epilayer on an r-plane (102) sapphire substrate, grown by low-pressure metal-organic vapour deposition is investigated by Raman spectroscopy. The room-temperature Raman scattering spectra of nonpolar a-plane GaN are measured in surface and edge backscattering geometries. The lattice is contracted in both the c- and the m-axis directions, and the stress in the m-axis direction is larger than that in the c-axis direction. On the surface of this sample, a number of cracks appear only along the m-axis, which is confirmed by the scanning electron micrograph. Atomic force microscopy images reveal a significant decrease in the root-mean-square roughness and the density of submicron pits after the stress relief.

Study of (Ga, Mn)N prepared by Mn-ion implantation using optical techniques

This paper reports that (Ga, Mn)N is prepared using implantation of 3at.% Mn Ions into undoped GaN. Structural characterization of the crystals was performed using x-ray diffraction(XRD). Detailed XRD measurements have revealed the characteristic of Mn-ion implanted GaN with a small contribution of other compounds. With Raman spectroscopy measurements, the spectra corresponding to the intrinsic GaN layers demonstrate three Raman active excitations at 747, 733 and 566 cm-1 identified as E1(LO), A1(LO) and E2H, respectively. The Mn-doped GaN layers exhibit additional excitations at 182, 288, 650-725, 363, 506 cm-1 and the vicinity of E2H mode. The modes observed at 182, 288, 650-725 cm-1 are assigned to macroscopic disorder or vacancy-related defects caused by Mn-ion implantation. Other new phonon modes are assigned to Mnx-Ny, Gax-Mny modes and the local vibrational mode of Mn atoms in the (Ga, Mn)N, which are in fair agreement with the standard theoretical results.

Activation of Hydrogen-Passivated Mg in GaN-Based Light Emitting Diode Annealing with Minority-Carrier Injection

We discuss an issue on the activation of p-GaN material under different annealing conditions and study the mechanism for the p-GaN activation. Under annealing in nitrogen, it is found that hydrogen cannot be completely removed from p-GaN. The experiments also indicate that rudimental hydrogen can exist stably in a certain state where hydrogen does not passivate the Mg acceptor in the sample annealing under bias. However, making additional annealing in nitrogen, we find that the steady state hydrogen can be decomposed and the Mg–H complex could generate again. Hydrogen remaining in the layer seems to play a major role in this reversible phenomenon.

Influence of dislocations in the GaN layer on the electrical properties of an AlGaN/GaN heterostructure

This paper reports on a comparative study of the spatial distributions of the electrical, optical, and structural properties in an AlGaN/GaN heterostructure. Edge dislocation density in the GaN template layer is shown to decrease in the regions of the wafer where the heterostructure sheet resistance increases and the GaN photoluminescence band-edge energy peak shifts to a high wavelength. This phenomenon is found to be attributed to the local compressive strain surrounding edge dislocation, which will generate a local piezoelectric polarization field in the GaN layer in the opposite direction to the piezoelectric polarization field in the AlGaN layer and thus help to increase the two-dimensional electron gas concentration.