Metalorganic Hydride Vapor-phase Epitaxy Research Articles

Hydride Vapor-Phase Epitaxy of a Semipolar AlN(10$$\bar {1}$$2) Layer on a Nanostructured Si(100) Substrate

We propose a method for the synthesis of hexagonal AlN layer on Si(100) substrate with a V-groove nanostructured surface where the angle between the sloped nanoridge surface and Si(100) plane amounts to 47°. It is established that metalorganic hydride vapor-phase epitaxy (HVPE) on this substrate leads to the formation of semipolar AlN(10$$\bar {1}$$2) layers having an X-ray rocking curve with a minimum FWHM value of ωθ ~ 60 arcmin. Raman spectra of this epilayer display additional peaks related to A1(TO) and E1(TO) phonons in contrast to the spectrum of a polar AlN(0001) layer containing an additional A1(LO) peak.

Semipolar GaN Layers Grown on Nanostructured Si(100) Substrate

We propose a new method for growing semipolar GaN films on a Si(100) substrate with an array of sub-100-nm-sized V-grooves formed on the surface. It is shown that, using such a nanostructured substrate for metalorganic hydride vapor-phase epitaxy, it is possible to obtain GaN (1011) epilayers deviating by an angle of about 62° from the polar direction and having an X-ray rocking curve with a minimum FWHM value of ωθ ~ 60 arcmin.

Strain relaxation in multilayer III–N structures on Si(111) substrates

X-ray diffractometry and X-ray scattering reciprocal space maps have been used to study strain relaxation in a complex buffer composed of seven intermediate layers of AlxGa1 − xN composition with different values of x, decreasing with an increase in the distance from the substrate. The layers have been grown by hydride metalorganic vapor phase epitaxy on silicon and sapphire substrates. Differences in the structural quality of the first four layers of a multilayer buffer grown on different substrates have been revealed. A gradual smoothing out of these differences in the next three layers with an increase in the layer serial number has been shown. The last grown intermediate AlxGa1 − xN layer and the GaN layer grown on it have identical thicknesses and degrees of mosaicity, regardless of the substrate type. Device structures grown on a complex buffer demonstrate emission in approximately the same wavelength range.

850-nm diode lasers based on AlGaAsP/GaAs heterostructures

Laser heterostructures with waveguides and emitter layers made of AlGaAs and AlGaAsP alloys are grown by hydride metal-organic vapor-phase epitaxy on a GaAs substrate and studied. It was shown that the heterostructure containing AlGaAsP layers has a large curvature radius in comparison with the structure consisting of AlGaAs layers. Ridge waveguide lasers with an aperture of 100 μm are fabricated based on the AlGaAsP/GaAs laser heterostructure and studied. The internal optical loss of the lasers is 0.75 cm−1; the characteristic parameter T0 = 140 K in the temperature range of 20–70°C. The maximum optical output power per mirror reached 4.1 W; cw lasing was retained at a heat sink temperature of 120°C.

Study of minority carrier diffusion lengths in photoactive layers of multijunction solar cells

A technique for determining a minority carrier’s diffusion length in photoactive III–V layers of solar cells by approximating their spectral characteristics is presented. Single-junction GaAs, Ge and multi-junction GaAs/Ge, GaInP/GaAs, and GaInP/GaInAs/Ge solar cells fabricated by hydride metal-organic vapor-phase epitaxy (H-MOVPE) have been studied. The dependences of the minority carrier diffusion length on the doping level of p-Ge and n-GaAs are determined. It is shown that the parameters of solid-state diffusion of phosphorus atoms to the p-Ge substrate from the n-GaInP nucleation layer are independent of the thickness of the latter within 35–300 nm. It is found that the diffusion length of subcells of multijunction structures in Ga(In)As layers is smaller in comparison with that of single-junction structures.

Two-band lasing in epitaxially stacked tunnel-junction semiconductor lasers

Epitaxially stacked tunnel-junction laser hetero structures were grown by hydride metalorganic vapor-phase epitaxy in the system of AlGaAs/GaAs/In GaAs alloys. Based on such structures, mesa stripe lasers with an aperture of 150 s- 7 m were fabricated. The possibility of controlling the lasing wavelength by varying the active region thickness in each tunnel-junction laser structure was demonstrated. Independent two-band lasing at wavelengths of 914 and 925 nm (the difference frequency is 2.3 THz) was achieved at a maximum optical radiation power of 20 W in each band of the epitaxially stacked tunnel-junction semiconductor laser.

Pulsed semiconductor lasers with higher optical strength of cavity output mirrors

Asymmetric heterostructures with an ultrathick waveguide based on an AlGaAs/GaAs alloy system that allow lasing at a wavelength of 905 nm have been developed and fabricated by hydride metalorganic vapor-phase epitaxy. The internal optical loss and internal quantum efficiency of semiconductor lasers based on such structures were 0.7 cm-1 and 97%, respectively. It is shown that the highest output optical power of laser diodes with antireflecting (SiO2) and reflecting (Si/SiO2) coatings deposited on untreated Fabry-Perot cavity facets obtained by cleaving in an oxygen atmosphere reached 67 W in the pulsed mode and is limited by mirror damage. Treatment of Fabry-Perot cavity facets by etching in argon plasma and the formation of coatings with passivating and oxygen-blocking GaN and Si3N4 layers allowed an increase in the maximum output optical power to 120 W. Mirror damage was not observed at the attained output optical power.

InN Nanorods Grown on Different Planes of Al2O3

Extract Extended abstract of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

InN Nanostructured Materials: Controlled Synthesis, Characterizations, and Applications

InN 1D materials were successfully grown by metal-organic vapor phase epitaxy (MOVPE) and non-catalytic, template-free hydride metal-organic vapor phase epitaxy (H-MOVPE) on Si, GaN, and c-Al2O3 substrates. Dislocation-free, high-quality InN nanorods with [00.1] growth axis were formed via an apparent vapor-solid (VS) growth mechanism by H-MOVPE. On a contrary when conventional MOVPE was employed InN nanowires were grown via vapor-liquid-solid (VLS) mechanism. The controlled growth of self-seeded III-Nitride nanostructured materials has been demonstrated.

Growth of InN films and nanorods by H-MOVPE

InN films and nanorods were grown by hydride metalorganic vapor phase epitaxy (H-MOVPE) and the effects of growth temperature, and NH 3/TMIn and HCl/TMIn ratios on morphological dependences were studied. The growth habit of InN varied from thin film to microrod to nanorod to no deposition as the growth conditions were changed about transition from growth to etching conditions. The growth and etch regimes were also predicted by chemical equilibrium calculations of In–C–H–Cl–N-inert system. The optical properties of InN nanorods and columnar structured films were measured by room temperature PL and a maximum intensity was observed at 1.08 eV for both structures.

Studying the characteristics of pulse-pumped semiconductor 1060-nm lasers based on asymmetric heterostructures with ultrathick waveguides

High-power semiconductor lasers based on asymmetric quantum-dimensional separate confinement InGaAs/GaAs heterostructures with ultrathick waveguides were fabricated by means of metalorganic hydride vapor phase epitaxy technology. The laser characteristics were studied in a pulsed pumping regime, in which the emission was excited by current pulses of 100 ns duration at a repetition frequency of 10 kHz and an amplitude of up to 200 A. The passage to a pulsed lasing regime allowed the active region heating to be reduced and the output power to be increased to 145 W for a laser diode with a 100-μm exit aperture. The results obtained for the pulsed lasing regime show that saturation of the output power-current characteristic observed in the continuous-wave regime is fully determined by overheating of the active region of a semiconductor laser.

High efficiency and brightness of blue light emission from dislocation-free InGaN∕GaN quantum well nanorod arrays

We report on the optical properties of blue-light-emitting, dislocation-free InGaN∕GaN multiple quantum well (MQW) nanorod arrays (NRAs) with high brightness and high efficiency. The InGaN MQW NRAs were grown by metal-organic hydride vapor phase epitaxy and the optical properties were investigated in detail by photoluminescence (PL), PL excitation (PLE) and time resolved PL. We observed a large Stokes-like shift between InGaN PL emission and PLE absorption edge due to the influence of built-in internal electrical field, reflecting the coherent growth of MQW along the NRA growth direction. From the temperature-dependent PL, we extracted a PL intensity ratio at 300to15K of ∼55.4% and large thermal activation energy of ∼171meV from the InGaN∕GaN MQW NRAs. Time-resolved PL results showed almost the same decay time of the InGaN emission at 20 and 300K. From the results, the optical properties are dominated by the radiative recombination process and are insensitive to temperature due to large thermal activation energy, indicating that carriers in InGaN wells are well confined by the GaN barriers without an influence of other non-radiative processes. Therefore, we conclude that internal quantum efficiency and extraction efficiency of MQW NRAs are significantly enhanced by a drastic suppression of non-radiative centers inside NRAs and a large surface area to active volume area ratio of NRAs, respectively.

Growth of thick GaN on the (0001) Al 2O 3 substrate by hydride-metal organic vapor phase epitaxy

We report on the crystal quality of thick GaN layers grown on (0001) Al 2O 3 substrates by newly developed hydride-metal organic vapor phase epitaxy (H-MOVPE) technique. The effects of process parameters on the growth rate were investigated, and the highest growth rate was achieved to be ∼ 90 μm/h. The X-ray diffraction measurements showed that the layer grown by H-MOVPE on (0001) Al 2O 3 without any buffer layer has good crystallinity with rocking curve FWHM of the (0002) reflection of about 500 arcsec. Films grown with LT-GaN seed layer of ∼ 20 nm thickness showed excellent surface morphology with rocking curve FWHM of the (0002) reflection of about 300 arcsec. The photoluminescence spectra of the films showed a strong band edge emission at 3.47 eV with a FWHM of 54 meV at room temperature, indicating the thick GaN layer grown on (0001) Al 2O 3 with LT-GaN seed layer is of device-grade quality.

Pt-coated InN nanorods for selective detection of hydrogen at room temperature

Single crystal InN nanorods were successfully grown on c-Al2O3 by hydride-metalorganic vapor phase epitaxy. The measured resistance of bare InN nanorods does not change upon exposure to hydrogen ambient. The addition of sputter-deposited clusters of Pt onto the surface of the InN nanorods, however, produced a significant change in the measured room temperature resistance. The measured resistance changed systematically by 0.5%–12% as the ambient hydrogen concentration in N2 was varied between 10 and 250 ppm after 15 min exposure time. Importantly, a relatively low power consumption of ∼0.3mW was measured under these conditions. There was no response at room temperature to O2, N2O, or NH3 exposures.

Growth and characterization of single-crystalline gallium nitride using (1 0 0) LiAlO 2 substrates

Self-separating single-crystalline gallium nitride films were grown by hydride-metalorganic vapor-phase epitaxy (H-MOVPE) on LiAlO 2 (LAO) substrates. Nitridation of the LAO substrate leads to the reconstruction of the surface and to the formation of a thin layer of nitrided material. Free-standing films of 35–40 μm thick were grown by a succession of techniques using both MOVPE and hydride vapor-phase epitaxy (HVPE) growth steps. The films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and micro-Raman spectroscopy to investigate the effect of the initial MOVPE step.

High-Brightness Light Emitting Diodes Using Dislocation-Free Indium Gallium Nitride/Gallium Nitride Multiquantum-Well Nanorod Arrays

We demonstrate the realization of the high-brightness and high-efficiency light emitting diodes (LEDs) using dislocation-free indium gallium nitride (InGaN)/gallium nitride (GaN) multiquantum-well (MQW) nanorod (NR) arrays by metal organic-hydride vapor phase epitaxy (MO−HVPE). MQW NR arrays (NRAs) on sapphire substrate are buried in spin-on glass (SOG) to isolating individual NRs and to bring p-type NRs in contact with p-type electrodes. The MQW NRA LEDs have similar electrical characteristics to conventional broad area (BA) LEDs. However, due to the lack of dislocations and the large surface areas provided by the sidewalls of NRs, both internal and extraction efficiencies are significantly enhanced. At 20 mA dc current, the MQW NRA LEDs emit about 4.3 times more light than the conventional BA LEDs, even though overall active volume of the MQW NRA LEDs is much smaller than conventional LEDs. Moreover, the fabrication processes involved in producing MQW NRA LEDs are almost the same for conventional BA LEDs. It is, thus, not surprising that the total yield of these MQW NRA LEDs is essentially the same as that of conventional BA LEDs. The present method of utilizing dislocation-free MQW NRA LEDs is applicable to super-bright white LEDs as well as other semiconductor LEDs for improving total external efficiency and brightness of LEDs.

Laser diodes (λ=0.98 μm) with a narrow radiation pattern and low internal optical losses

Quantum-confined InGaAs/AlGaAs/GaAs heterostructures for laser diodes emitting at λ=0.98 μm, optimized to provide for reduced radiation divergence in the vertical plane and decreased internal optical losses, have been synthesized by metalorganic-hydride vapor-phase epitaxy. For the obtained laser diodes the far field pattern full width at half-maximum in the vertical plane falls within 16°–19°, the internal optical losses are about 0.7 cm−1, the internal quantum yield amounts to 97%, and the maximum continuous emission power reaches 8.6 W.

High-power 1.7–1.8 μm single-mode laser diodes

Separate confinement InGaAsP/InP laser heterostructures were grown by metalorganic-hydride vapor-phase epitaxy. High-power single-mode laser diodes of mesastripe design based on these heterostructures operate in a wavelength interval of 1.7–1.8 μm with a maximum continuous room temperature output power of 150 mW. The single-mode lasing regime is maintained up to an output power level of 100 mW.

GaN Grown by Hydride - Metal Organic Vapor Phase Epitaxy (H-MOVPE) on Lattice-Matched Oxide and Silicon Substrates

GaN Grown by Hydride - Metal Organic Vapor Phase Epitaxy (H-MOVPE) on Lattice-Matched Oxide and Silicon Substrates

Large area GaN substrates

Free-standing GaN substrates were fabricated by hydride-metal organic vapor phase epitaxy (H-MOVPE) on closely lattice-matched LiGaO 2 substrates. The key to obtaining GaN films on LiGaO 2 was the initial surface nitridation step. Nitriding and cooling processes were found to be critical film–substrate self-separation. The GaN surface morphology of the GaN was determined by AFM; the structural quality was analyzed by XRD; the chemical composition was investigated by AES, ESCA, and SIMS. Raman spectroscopy was applied for film and substrate characterization.