Molecular-beam epitaxy of GaN/AlxGa1−xN multiple quantum wells on R -plane (101̄2) sapphire substrates

In the epitaxial lateral overgrowth (ELO) of (1120) a-plane GaN, the uneven growth rates of two opposing wings, Ga-and N-wings, makes the coalescence of two neighboring wings more difficult than that in c-plane GaN. We report a two-stage growth method to get uniformly coalesced epitaxial lateral overgrown a-plane GaN using metalorganic chemical vapor deposition (MOCVD) by employing relatively lower growth temperature in the first step followed by enhanced lateral growth in the second. Using this method, the height differences between Ga-polar and N-polar wings at the coalescence front could be reduced, thereby making the coalescence of two wings much easier. Transmission electron microscopy (TEM) showed that the threading dislocation density in the wing areas was 1.0×10 8 cm -2 , more than two orders of magnitude lower than that in the window areas (4.2×10 10 cm -2 ). However, high density of basal stacking faults of 1.2×10 4 cm -1 was still observed in the wing areas as compared to c-plane GaN. Atomic force microscopy and photoluminescence

Section: Introductionmentioning

confidence: 99%

Defect reduction in (112¯) a-plane GaN by two-stage epitaxial lateral overgrowth

Özgür

et al. 2006

“…[1][2][3][4][5] Unlike conventional c-plane quantum wells, nonpolar ͑a-and m-plane͒ quantum wells are free of polarization-related electric fields along the growth direction. 6,7 However, heteroepitaxially grown planar a-plane GaN films are characterized by the presence of high dislocation density due to the large lattice mismatch with the available substrates.…”

mentioning

confidence: 99%

Defect reduction in nonpolar a-plane GaN films using in situ SiNx nanomask

Chakraborty

Kim

et al. 2006

112

106

We report on the use of in-situ SiNx nanomask for defect reduction in nonpolar a-plane GaN films, grown by metal-organic chemical vapor deposition. High-resolution x-ray diffraction analysis revealed that there was a monotonic reduction in the full width at half maximum, both on-axis and off-axis, with the increase in the SiNx thickness. Atomic force microscopy images revealed a significant decrease in the root-mean-square roughness and the density of submicron pits. Cross-section and plan-view transmission electron microscopy on the samples showed that the stacking fault density decreased from 8×105to3×105cm−1 and threading dislocation density decreased from 8×1010to9×109cm−2. Room temperature photoluminescence measurement revealed that the band-edge emission intensity increased with the insertion of the SiNx layer, which suggests reduction in the nonradiative recombination centers.

“…1, 2 In an effort to eliminate the effects of internal polarization-induced electric fields, wurtzite group III nitride films have been grown in the a-plane ͑1120͒ and m-plane ͑1010͒ orientations. 3,4 These growth directions orient the polarization in the plane of heterointerface and, thus, there are no polarization-related electric fields in laterally uniform devices. Plasma-assisted molecular-beam epitaxy ͑PAMBE͒-grown c-face GaN suffers from a second deleterious effect in that doping with the commonly used acceptor Mg at high concentrations or low III/V ratios often results in the formation of inversion domains that degrade the quality of the crystal.…”

mentioning

confidence: 99%

Molecular-beam epitaxy of p-type m-plane GaN

McLaurin

Mates

Speck

2005

139

We report on the plasma-assisted molecular-beam epitaxy of Mg-doped ͑1010͒ GaN on ͑1010͒ 6H-SiC. Secondary ion mass spectroscopy measurements show the incorporation of Mg into the GaN films with an enhanced Mg incorporation under N-rich conditions relative to Ga-rich growth. Transport measurements of Mg-doped layers grown under Ga-rich conditions show hole concentrations in the range of p =1ϫ 10 18 to p =7ϫ 10 18 cm −3 and a dependence between hole concentration and Mg beam equivalent pressure. An anisotropy in in-plane hole mobilities was observed, with the hole mobility parallel to ͓1120͔ being higher than that parallel to ͓0001͔ for the same hole concentration. Mobilities parallel to ͓1120͔ were as high as ϳ11.5 cm 2 /Vs ͑at p ϳ 1.8 ϫ 10 18 cm −3 ͒.