Hun Kang

Manganese-induced long-range lattice disorder and vacancy formation in metal-organic chemical vapor deposition grown and ion-implanted Ga1−xMnxN

The structural properties and lattice dynamics of Ga1−xMnxN were studied for Mn concentrations from 0.0% to 1.5%. Ga1−xMnxN layers were fabricated by either Mn incorporation during the metal-organic chemical vapor deposition (MOCVD) growth process or by postgrowth ion implantation into MOCVD-grown GaN epilayers. The crystalline integrity and the absence of major second phase contributions were confirmed by high-resolution x-ray diffraction analysis. Raman spectroscopy showed that increased Mn incorporation in the epilayers significantly affected long-range lattice ordering, revealing a disorder-induced mode at 300cm−1 and a local vibrational mode at 669cm−1. The low intensities of both modes were shown to scale with Mn concentration. These observations support the formation of nitrogen vacancies, even under optimized MOCVD growth conditions. The slight excess of metal components in the growth process compared to undoped GaN growth and the incorporation of Mn deep acceptor levels favors the formation of ni...

X-Ray Diffraction Analysis of GaN and AlGaN

In this paper, threading dislocation densities in GaN and AlGaN epitaxial layers have been evaluated using two different X-ray analysis techniques; a Williamson Hall (WH) plot and reciprocal space mapping (RSM). GaN and AlGaN have crystalline growth composed of columnar structures that can be estimated by coherence length and angular misorientation measured by X-ray. A WH plot can provide information about coherence length and tilt angle from a linear fit to the linewidth of the triple axis rocking curve (000 l ) symmetric reflections. RSM is typically used to obtain this data, but it is more involved in technique. The two dominant components of threading dislocation densities (screw and edge types) in the GaN and AlGaN epitaxial layers were found to be similar by both techniques. The treading dislocation density correlates to the size of columnar structure as determined by coherence length, tilt angle, and twist angle. The effect of Al composition in AlGaN alloys on these dislocation densities was investigated and found to depend on strongly on the type of nucleation layer, GaN or AlN.

The growth of InN and related alloys by high-pressure CVD

The growth of high-quality InN and indium rich group III-nitride alloys are of crucial importance for the development of high-efficient energy conversion systems, THz emitters and detectors structures, as well as for high-speed linear/nonlinear optoelectronic elements. However, the fabrication of such device structures requires the development of growth systems with overlapping processing windows in order to construct high-quality monolithic integrated device structures. While gallium and aluminum rich group III-nitrides are being successfully grown by organometallic chemical vapor deposition (OMCVD), the growth of indium rich group III-nitrides presents a challenge due to the high volatility of atomic nitrogen compared to indium. In order to suppress the thermal decomposition at optimum processing temperatures, a new, unique high-pressure chemical vapor deposition (HPCVD) system has been developed, allowing the growth of InN at temperatures close to those used for gallium/aluminum-nitride alloys. The properties of InN layers grown in the laminar flow regime with reactor pressures up to 15 bar, are reported. Real-time optical characterization techniques have been applied to analyze gas phase species and are highly sensitive the InN nucleation and steady state growth, allowing the characterization of surface chemistry at a sub-monolayer level. The ex-situ analysis of the InN layers shows that the absorption edge in the InN shifts below 0.7 eV as the ammonia to TMI precursor flow ratio is lowered below 200. The results indicate that the absorption edge shift in InN is closely related to the In:N stoichiometry.

X-ray diffraction analysis of threading dislocation densities in epitaxial layers as grown by MOCVD

Summary form only given. Threading dislocation densities in epitaxial layers were evaluated using two different X-ray analysis techniques: Williamson Hall (WH) plots and reciprocal space mapping (RSM). The crystalline epitaxial layers were grown by MOCVD. They were composed of columnar structures that can be estimated by coherence length and angular misalignment. The RSM technique, depending on the scanning point, is capable of providing unique information with respect to these columnar structures. On the other hand, a WH plot can provide on overall mean value of the metrics for crystalline structures. Two dominant types (screw and edge) of threading dislocation densities in the epitaxial layers were found by both techniques. The dislocation densities in the epitaxial layers were found to depend strongly on the type and thickness of GaN or AlN nucleation layer.