The growth of InGaN/AlGaN multiple quantum wells (MQWs) structures is highly effective for realizing high quality semipolar ($20\bar{2}1$) active regions for green light emitting diodes (LEDs) and ...laser diodes (LDs). The use of AlGaN barriers significantly improved internal quantum efficiencies and the uniformity of the emission compared to InGaN or GaN barriers. 516 nm lasing wavelength was demonstrated on semipolar ($20\bar{2}1$) GaN substrates by introducing three periods InGaN/AlGaN MQWs and the AlGaN-cladding-free optical waveguide consisting of GaN cladding and InGaN guiding layers.
We compare facet morphology, device characteristics, and far field patterns (FFPs) for semipolar (112̅2) laser diodes fabricated with mechanically polished and dry etched mirror facets. Facets formed ...by Cl2-based dry etching produced inclined and heavily striated facets. Mechanically polished facets, in contrast, provided vertical and smooth facets (rms roughness=5.2 nm). The threshold currents of polished facet devices were on average ~ 100 and ~ 200 mA lower than etched facet devices (2 × 1200 μm 2 and 4 × 1200 μm 2 dimension devices, respectively). FFPs from etched facets were also shown to be obscured due to substrate reflections.
Local excitation and emission dynamics of an isolated "Type-I1 basal-plane stacking-fault (BSF) in very low dislocation density GaN were studied using spatio-time-resolved cathodoluminescence. The ...low temperature lifetime of the BSF emission was quantified to be 640 ps. The carrier diffusion length was estimated by observing the temporal delay of the BSF peak relative to the free-exciton signal as a function of distance from the BSF. The results indicate that the near-band-edge emission leads to subsequent optical excitation of the BSF that increases the apparent diffusion length. Limiting the observation volume can improve the spatial resolution.
Fundamental electronic and optical properties of a low-resistivity m-plane GaN single crystal, which was grown by hydride vapor phase epitaxy on a bulk GaN seed crystal synthesized by the ...ammonothermal method in supercritical ammonia using an acidic mineralizer, were investigated. The threading dislocation and basal-plane staking-fault densities of the crystal were around 104 cm−2 and less than 100 cm−1, respectively. Oxygen doping achieved a high electron concentration of 4 × 1018 cm−3 at room temperature. Accordingly, a photoluminescence (PL) band originating from the recombination of hot carriers was observed at low temperatures, even under weak excitation conditions. The simultaneous realization of low-level incorporation of Ga vacancies (VGa) less than 1016 cm−3 was confirmed by using the positron annihilation technique. Consistent with our long-standing claim that VGa complexes are the major nonradiative recombination centers in GaN, the fast-component PL lifetime of the near-band-edge emission at room temperature longer than 2 ns was achieved.
Effects of
off-axis substrates on
m-plane InGaN/GaN light-emitting diodes (LEDs) grown by metal organic chemical vapor deposition were investigated. The surface morphology of n-GaN was improved by ...increasing an
off-axis angle from the
m-plane toward the
c-plane. The InGaN/GaN quantum wells (QWs) grown on the
off-axis substrates toward the
c
−
-direction (
N-polar) emitted at a longer peak wavelength than the
on-axis
m-plane substrates, indicating that the
off-axis substrates have impact on enhancement of the indium incorporation in the InGaN/GaN QWs. The LED on the
c
−
-5°
off-axis substrate emitted at 457
nm under DC current of 20
mA and showed 0.7
nm red-shift from 1 to 20
mA. The
c
−
-5°
off LED showed an optical polarization ratio of 0.91, which is comparable to the nonpolar material.
Bulk GaN crystals grown by HVPE Fujito, Kenji; Kubo, Shuichi; Nagaoka, Hirobumi ...
Journal of crystal growth,
05/2009, Letnik:
311, Številka:
10
Journal Article, Conference Proceeding
Recenzirano
We succeeded in preparing very thick
c-plane bulk gallium nitride (GaN) crystals grown by hydride vapor phase epitaxy. Growth of the bulk GaN crystals was performed on templates with 3
μm GaN layer ...grown by metal organic chemical vapor deposition on (0
0
0
1) sapphire substrates. Colorless freestanding bulk GaN crystals were obtained through self-separation processes. The crystal's diameter and thickness were about 52 and 5.8
mm, respectively. No surface pits were observed within an area of 46
mm diameter of the bulk GaN crystal. The dislocation density decreased with growth direction (from N-face side to Ga-face side) and ranged from 5.1×10
6
cm
−2 near the N-face surface to 1.2×10
6
cm
−2 near the Ga-face. A major impurity was Si, and other impurities (O, C, Cl, H, Fe, Ni and Cr) were near or below the detection limits by SIMS measurements.
We demonstrate the first electrically-injected InGaN/GaN laser diodes (LDs) grown on semipolar $(30\bar{3}1)$ free-standing GaN substrates. The lowest threshold current density ($J_{\text{th}}$) was ...5.6 kA/cm 2 with a clear lasing peak at 444.7 nm. The peak electroluminescence (EL) wavelength blue-shifted 4 nm below threshold and the characteristic temperature was ${\sim}135$ K. These results suggest that the semipolar $(30\bar{3}1)$ plane may be a potential candidate for growing high performance nitride-based LDs.
