Pressure Organometallic Vapor Phase Epitaxy Research Articles

Optically pumped room temperature low threshold deep UV lasers grown on native AlN substrates

We report here an optically pumped deep UV edge emitting laser with AlGaN multiple quantum wells (MQWs) active region grown on AlN substrate by low pressure organometallic vapor phase epitaxy (LP-OMVPE) in a high-temperature reactor. The 21 period Al_0.53Ga_0.47N/Al_0.7Ga_0.3N MQWs laser structure was optically pumped using 193 nm deep UV excimer laser source. A laser peak was achieved from the cleaved facets at 280.3 nm with linewidth of 0.08 nm at room temperature with threshold power density of 320 kW/cm². The emission is completely TE polarized and the side mode suppression ratio (SMSR) is measured to be around 14 dB at 450 kW/cm².

X-ray characterization of composition and relaxation of AlxGa1−xN(≤x≤1) layers grown on GaN/sapphire templates by low pressure organometallic vapor phase epitaxy

A characterization procedure was developed to determine the alloy composition and strain state of AlxGa1−xN/GaN(0<x<1) heterostructures deposited on c-plane sapphire substrates by low pressure organometalic vapor phase epitaxy. Motivated by a method suggested by Bowen and Tanner for separating the contributions of strain and composition in cubic crystals, we extended the technique to the case of hexagonal crystals by first principles derivation from elastic strain theory. The technique was evaluated using double-axis and triple-axis reciprocal space maps of 200 and 30 nm AlxGa1−xN layers. The procedure did not require absolute lattice parameter measurements and relied instead on relative measurements of the layer and substrate peak positions. Symmetric and asymmetric reflections of the film and substrate were measured in the double-axis configuration with ω–2θ scans. From the peak separation, the strained lattice parameters were determined. Assuming biaxial strain and linear variation of the relaxed lattice parameter with alloy composition, an equation was derived for composition in terms of the strained lattice parameters. The relaxation distribution in the AlGaN was found to be bimodal. Films with mole fraction of Al greater than 0.4 were completely relaxed and thoroughly cracked, while films with mole fraction of Al less than 0.4 exhibited compositionally dependent relaxation about the fully strained state.

Improved luminescence properties of Eu-doped GaN light-emitting diodes grown by atmospheric-pressure organometallic vapor phase epitaxy

We investigated the luminescence properties of Eu-doped GaN (GaN:Eu) grown by atmospheric-pressure organometallic vapor phase epitaxy. The GaN:Eu exhibited radiant red emission due to the intra-4f shell transition of Eu3+ ions at room temperature. The intensity of the dominant peak was about 4 times higher than that in the sample grown at 10 kPa, even though the Eu concentration was only half that of the 10 kPa sample. This was mainly caused by the enhancement of the energy transfer from the GaN host to Eu ions. The enhanced energy transfer resulted in improved luminescence properties of a GaN:Eu light-emitting diode.

Evidence of the De-multiplication Interactions Between Threading Dislocations in GaN Films Grown on (0001) Sapphire Substrates

AbstractWe report the observation of threading dislocation de-multiplication process by transmission electron microscopy (TEM). The GaN films used in this study were grown on (0001) sapphire substrates with LT-GaN buffer layers by reduced pressure organometallic vapor phase epitaxy. By using g · Db = 0 invisibility criterion, it was found that some of TDs were de-multiplicated by interactions among themselves. In particular, type a+c TDs were found to nucleate through the interactions between type a and type c TDs in GaN near the GaN/sapphire interface so that the de-multiplication of TDs in GaN films was achieved.

Reduction of oxygen contamination in AlN

High quality AlN thin films were grown by Low Pressure Organometallic Vapor Phase Epitaxy(LP-OMVPE) on sapphire and Si substrates. oxygen contamination in the Al layers can be reduced drastically by fine tuning of the growth parameters, by avoiding O-containing substrates, and by using a cap GaN layer. AlN films grown on Si, exhibiting oxygen concentration levels of [O] ≤ 1019 cm−3, display an X-Ray Diffraction Full Width Half Maximum (FWHM) of 190 arcsec and an extremely sharp near band-edge cathodoluminescence emission at 5.925 eV with FWHM of 30 meV and 5.975 eV (unresolved). (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Organometallic vapor phase epitaxy of GaN on Si(1 1 1) with a γ-Al 2O 3(1 1 1) epitaxial intermediate layer

Heteroepitaxial growth of GaN on Si(1 1 1) substrate was investigated by atmospheric pressure organometallic vapor-phase epitaxy. High-quality GaN layers on Si were deposited using an epitaxially grown intermediate layer of γ-Al 2O 3. The orientation relationship was found to be GaN(0 0 0 1)/γ-Al 2O 3(1 1 1)/Si(1 1 1) and GaN[1 1 2 ̄ 0]∥ γ-Al 2 O 3[ 1 ̄ 1 0]∥ Si[ 1 ̄ 1 0] . GaN layers with (0 0 0 2) rocking curve line width of 1000 arcsec have been obtained.

Growth and Performance Study of Aluminum-Free InGaAs/GaAs/InGaAsP Strained Quantum-Well Pump Lasers

The growth of InGaP, InGaAs and InGaAsP epilayers lattice matched to GaAs using the low pressure organometallic vapor phase epitaxy (LP-OMVPE) system was investigated. For the application of erbium-doped fiber amplifiers (EDFAs), the emission wavelength and far-field pattern of the pump laser were designed. The optical and electrical performances of the resultant pump laser were measured.

Microstructural evolution in a multiple composite layer of GaN on sapphire by organometallic vapor phase epitaxy

Using cross-section transmission electron microscopy and grazing incidence x-ray diffraction measurements, this work investigates the defect reduction in a wurtize GaN thin film with a multiple composite layer grown by atmospheric-pressure organometallic vapor phase epitaxy on sapphire substrate. According to those results, the sequential composite layer can terminate most threading dislocations and only a few dislocations can be deeply propagated into the next epitaxial layer. Moreover, the multiple composite layer structure significantly reduces the density of threading dislocation generated from the GaN/Al2O3 interface.

Effects of multiple buffer layers on structural electronic properties of GaN growth by atmospheric pressure Organometallic Vapor Phase Epitaxy

High-quality GaN epitaxial films have been grown on sapphire by organometallic vapor phase epitaxy using multiple-pair buffer layers. Each pair of buffer layers consists of a thin GaN nucleation layer grown at a low temperature around 500°C and a thick GaN epitaxial layer around 4 μm thick grown at a high temperature around 1000°C. The sample with four-pair buffer layers showed much improved GaN epitaxial films, as compared to the sample with only one-pair of buffer layers. The better qualities include narrower full width at half maximum of 150 arc-s and stronger intensity in double-crystal X-ray diffraction, higher electron mobility of 420 cm 2 V-s −1, lower background concentration of 3×10 17 cm −3, and lower etch-pit density of mid-10 5 cm −2.

Observation of high electric field at ZnSe/GaAs heterointerfaces by fast Fourier transformed photoreflectance

High electric fields at ZnSe/GaAs heterointerfaces grown by atmospheric-pressure organometallic vapor phase epitaxy (OMVPE) were revealed by fast Fourier-transformed photoreflectance (FFT-PR) measurements at room temperature. In the PR measurements, a modulation light was provided by a He-Ne laser exciting only GaAs regions at the interfaces. PR spectra were obtained with Franz–Keldysh oscillations (FKOs) above the band-gap energy of GaAs. FFT was successfully applied to the PR spectra to calculate the interface electric field from the FKOs. The observed electric fields were very high and in the range of 100–150 kV/cm. The dependence of the electric fields on the Zn- or Se-exposure duration showed a clear relationship with that of the valence-band offsets determined by X-ray photoemission spectroscopy (XPS). The resultant electric field was discussed in conjunction with the valence-band offsets.

Highly p-type carbon-doped InGaAs grown by atmospheric pressure organometallic vapor-phase epitaxy

Carbon doped, p-type, In x Ga 1− x As (0.2< x<0.65) epilayers have been grown on InP substrates at relatively low temperature (450°C) using atmospheric pressure organometallic vapor-phase epitaxy (APOMVPE). Excellent morphology was obtained in all cases. After growth van der Pauw–Hall measurements revealed high hole concentrations in the range 8.5×10 18–8.7×10 19 cm −3 (highest reported to date for APOMVPE). The effects of growth temperature, V/III ratio and CCl 4 partial pressure on the carrier concentration and mobility are reported. X-ray diffraction reveals excellent crystal quality. Annealing the samples in different ambients at 400–500°C caused no significant variation in the carrier concentration or mobility, i.e. minimal dopant ion passivation was measured. However, reversible hole compensation was measured after annealing at 650°C. This suggests that macroscopic defects probably are associated with carrier compensation.

Influences of initial nitridation and buffer layer deposition on the morphology of a (0001) GaN layer grown on sapphire substrates

Hexagonal GaN is grown on (0001) sapphire substrates using an atmospheric pressure organometallic vapor phase epitaxy method. We investigate the influences of the initial treatment of sapphire substrate, such as initial nitridation and low-temperature GaN buffer layer deposition, upon the surface morphology and crystallinity. The thermal stability of grown GaN layers is also investigated using a thermal etching process in a H2 atmosphere in order to obtain the information concerning the surface polarity of GaN(0001) layers. When sapphire substrates are initially nitrided, highly crystalline GaN layers with large hexagonal facets are obtained and its surface appears to be (0001)N. On the other hand, the deposition of a thicker buffer layer on the nitrided sapphire substrates improves the surface morphology, and the surface polarity of the mirror surface appears to be (0001)Ga. The initial nitridation of sapphire substrates and the GaN buffer layer deposition are considered to be important processes from viewpoints of the (0001) surface polarity.

Flow Modulation Epitaxial Lateral Overgrowth Of Gallium Nitride On Masked 6H-Silicon Carbide And Sapphire Surfaces

ABSTRACTSelective Area Flow Modulation Epitaxial growth of GaN is carried out in a low pressure Organometallic Vapor Phase Epitaxy reactor. This process is known to enhance reactant surface migration lengths on patterned group III-arsenide and phosphide growth surfaces. With this process, high quality laterally overgrown GaN epitaxial materials result. Under the ammonia rich growth conditions used, enhanced migration (by flux modulation) across masked regions of the substrate has not been observed. The mask materials were silicon dioxide and silicon nitride, both deposited on GaN/AlGaN buffer structures on sapphire and SiC substrates. Window stripes were patterned parallel and perpendicular to the (1100) crystal directions to observe the orientation dependence of the lateral growth rate. Structures exhibited heights above the mask surface as large as 30 microns and atomically smooth surfaces. With a periodic array of stripe window openings in the mask, planarized laterally overgrown surfaces are achieved after roughly 4 microns of overgrowth. Chemical assisted ion beam etching with chlorine gas was used to delineate defects in the selectively grown layers. Additional evidence on the defect reduction is given by Atomic Force and Scanning Transmission Electron Microscopies.

Photoluminescence characterization of GaN thin film grown by atmospheric pressure organometallic vapor phase epitaxy

Thin films of gallium nitride (GaN) were successfully prepared by our atmospheric pressure (AP) organometallic vapor phase epitaxy (OMVPE) system using GaN buffer layer over basal plane (0001) sapphire substrates. In the present study, strong band-edge photoluminescence (PL) in GaN films is observed. The variations of the growth temperature and ammonia/trimethylgallium (NH 3/TMG) mass flow ratio with the full width at half maximum (FWHM) of band-edge luminescence ( I BE, respectively, indicate that we could obtain ranges of the growth temperature and the NH 3/TMG ratio to have high quality GaN single crystal. The band-edge to deep-level luminescence ( I DL) ratio ( I BE/ I DL) also reveals that we could obtain optimized appropriate growth temperature and the supply of active nitrogen of excellent optical properties.

Low resistance bilayer Nd/Al ohmic contacts on n-type GaN

A bilayer Nd/Al metallization structure has been deposited onto low pressure organometallic vapor phase epitaxy grown n-type GaN ( 1 × 1018 cm−3) by electron-beam evaporation. Ohmic metal contacts were patterned photolithographically for standard transmission line measurement, and then thermally annealed at temperatures ranging from 200 to 350°C and from 500 to 650°C using conventional thermal annealing (CTA) and rapid thermal annealing (RTA), respectively. The lowest values for the specify contact resistivity of 9.8 × 10−6 Ω−cm2 and 8 × 10−6 Ω−cm2 were obtained using Nd/Al metallization with CTA of 250°C for 5 min and RTA of 600°C for 30 s. Examination of the surface morphology using atomic force microscopy as a function of annealing temperature revealed that the surface roughness was strongly influenced by conventional thermal annealing, it was smooth in the temperature range from 550 to 650°C for rapid thermal annealing. Auger electron spectroscopy depth profiling was employed to investigate the metallurgy and interdiffusion of contact formation.

Very high hole concentrations in C-doped InGaAs using new sources with APOMVPE

AbstractNew sources have been used to grow the first carbon doped, highly p-type InxGa1-xAs (0.2&gt;x&gt;0.7) epilayers on InP substrates by atmospheric pressure organometallic vapor phase epitaxy (APOMVPE). Excellent morphology was obtained simultaneously with high hole concentrations at growth temperatures near 450 °C. High hole concentrations of 1.6×1019 – 8.7×1019 cm−3 (the highest reported to date for APOMVPE), and the corresponding room temperature hole mobilities of 65 – 25 cm2/s, respectively, have been obtained from Hall measurements. X-ray diffraction is consistent with excellent crystal quality. Annealing at temperatures of T=400–500 °C in the presence of either nitrogen or hydrogen was found to change the carrier concentration by only 0–15%. However, after annealing at T=650 °C, irreversible changes occurred in the InGaAs. After a high temperature anneal, reversible order of magnitude changes in the hole concentration was obtained upon further annealing at low temperatures, depending upon the ambient. These results conclusively show that hydrogen does not passivate C acceptor ions in InGaAs. Since changes in the carrier concentration become substantial and reversible only after high temperature annealing, the results strongly suggest that a structural change occurred in the crystal at high temperatures. We consider it likely that this structural change is the precipitation of carbon out of a supersaturated solid solution, and that hydrogen atoms associated with these precipitates act as donors which compensate the hole concentration.

MOVPE growth optimization of high quality InGaN films.

In this paper growth of high quality InGaN films on (0001) sapphire substrates by atmospheric pressure organometallic vapour phase epitaxy in a vertical rotating disk reactor is investigated. The InGaN layers grown above 800 °C are transparent and show no In-droplets on the surface. The In-content varies between 56 and 9 % for growth temperatures between 700 and 850 °C. The DC X-ray rocking curve of InGaN typically shows a FWHM between 8 and 15 arcmin. Room temperature PL shows an intense band edge emission with a FWHM between 100 and 200 meV for an In-content of 9 and 56 %. The initial efforts on QW growth are discussed.

Diffraction-limited 1.3-μm-wavelength tapered-gain-region lasers with &gt;1-W CW output power

Diode lasers have been fabricated in InGaAsP-InP multiple-quantum-well material grown by atmospheric-pressure organometallic vapor-phase epitaxy with an active optical cavity consisting of a ridge-waveguide region coupled to a tapered gain region. Over 1 W of CW output power was obtained with 85% of the power in the central lobe of a diffraction-limited far-field radiation pattern.

Growth by OMVPE and X-ray analysis of ZnTe and [formula omitted] epilayers on III–V substrates

II–VI compounds are promising materials for optoelectronic applications. They are characterized by a large bandgap in the visible region, which allows the production of lasers and light emitting diodes in the blue region as the zinc telluride gap at room temperature is 2.26 eV. We studied the epitaxial growth of zinc telluride and zinc selenide epilayers on gallium arsenide, indium phosphide and gallium arsenide substrates by atmospheric pressure organo-metallic vapor phase epitaxy. We focused especially on the X-ray analysis of thin layer deformations. The relaxation of the deformation in ZnTe epilayers on InP substrates and ZnSe buffer is abrupt. We observed serious deformation of the thin layers on a GaSb substrate.

Low oxygen and carbon incorporation in AIGaAs using tritertiarybutylaluminum in organometallic vapor phase epitaxy

High-quality AIGaAs epilayers have been grown by low pressure organometallic vapor phase epitaxy with a new aluminum precursor tritertiarybutylaluminum (TTBAl). Layers grown at 650°C have a featureless mirror surface morphology and strong room temperature photoluminescence. Carbon was not detectable in chemical analysis by secondary ion mass spectroscopy, nor in low temperature (4K) photoluminescence spectra. Oxygen concentration in Al0.25Ga0.75As is as low as ∼2−3 × 1017 cm−3. Nominally undoped AIGaAs layers exhibit n-type conductiv-ity with electron concentrations at ∼ 1−1.5 × 1016 cm−3. A high degree of compo-sitional uniformity over 5 cm diam substrates (0.268 ±0.001) was obtained. These results indicate the potential for TTBA1 as an aluminum precursor for low temperature growth of Al-containing III-V alloys.