Ultraviolet luminescence of thin GaN films grown by radical-beam gettering epitaxy on porous GaAs(111) substrates

GaN films with a thickness of 0.1 μm were grown by radical-beam gettering epitaxy on porous GaAs(111) substrates. Excitonic luminescence bands are dominant in the photoluminescence spectra measured at 4.2 K. The energy positions of excitonic-band peaks are analyzed; as a result, it is concluded that there are stresses in the grown GaN films. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 11, 2003, pp. 1303–1304. Original Russian Text Copyright ? 2003 by Kidalov, Sukach, Revenko, Potapenko.     

Optical properties of gallium nitride bulk crystals grown by chloride vapor phase epitaxy

The optical properties of bulk crystals of gallium nitride grown by chloride vapor-phase epitaxy are investigated. It is shown that these crystals exhibit exciton luminescence bands. Analysis of the energy positions of the band maxima imply certain conclusions about the presence or absence of mechanical stresses in the bulk crystals of GaN obtained. Analysis of the luminescence spectra also reveals that the temperature dependence of the width of the GaN band gap E _g in the temperature range T=6–600 K is well described by the expression E _g (T)=3.51−7.4×10⁻⁴ T ²(T+600)⁻¹ eV. It is estimated that values of the free electron concentration in these crystals do not exceed 10¹⁸ cm⁻³. The optical characteristics of the bulk GaN crystals are compared analytically with literature data on bulk crystals and epitaxial layers of GaN grown by various methods. Fiz. Tekh. Poluprovodn. 33, 1173–1178 (October 1999)     

Flow modulation epitaxy of indium gallium nitride

InGaN layers were grown on GaN films by flow modulation epitaxy (FME) using the precursors trimethylgallium, trimethylindium, and ammonia. The indium composition of the FME grown layers was generally lower than of films grown under the same conditions in the continuous growth mode, but which had been of poor optical quality. The indium incorporation efficiency increased with decreasing ammonia flush time, increasing ammonia flow during group-III injection, and increasing group-III precursor injection time. Films grown under optimized conditions showed intense band edge related luminescence at room temperature up to a wavelength of 465 nm. Atomic force microscopy investigations revealed a strong dependence of the surface morphology of the InGaN films on the growth mode.     

Preparation of ZnO:N films by radical beam gettering epitaxy

ZnO:N epitaxial films are obtained by radical beam gettering epitaxy. The properties of the films are studied using X-ray diffraction, atomic-force microscopy, secondary-ion mass spectroscopy, and photoluminescence. A narrow (002) peak is observed in the X-ray diffraction spectra, which indicates that the ZnO:N films are oriented along the c axis. Secondary-ion mass spectroscopy indicates that N is present in the ZnO films. In the low-energy luminescence spectrum of the ZnO:N films, a peak at 3.31 eV is observed. This peak is presumably attributed to the exciton bound at the neutral acceptor N_O. The postannealing of the ZnO:N films was carried out in atomic oxygen. The nature of the donor-acceptor (3.23 eV) and green (2.56 eV) luminescence bands is discussed.     

Hydride vapor phase epitaxy for gallium nitride substrate

Due to the remarkable growth rate compared to another growth methods for gallium nitride(GaN)growth,hydride vapor phase epitaxy(HVPE)is now the only method for mass product GaN substrates.In this review,commercial HVPE systems and the GaN crystals grown by them are demonstrated.This article also illustrates some innovative attempts to develop homebuilt HVPE systems.Finally,the prospects for the further development of HVPE for GaN crystal growth in the future are also discussed.     

High-quality n-type aluminum gallium nitride thin films grown by interrupted deposition and in-situ thermal annealing

High quality Si-doped n-Al_0.6Ga_0.4N thin films were grown on sapphire substrates by molecular beam epitaxy (MBE) by interrupted deposition and subsequent in-situ thermal annealing (IDTA). High-resolution X-ray diffraction, scanning electron microscope, atomic force microscope, photoluminescence and Hall-effect measurements were carried out to characterize the structural, electrical and optical properties. The results showed that the full width at half-maximum of the Si-doped Al_0.6Ga_0.4N (0002) was as low as 160 arcsec. The threading dislocation density decreases two orders of magnitude to 6×110⁷ cm⁻² by using the IDTA technology. The carrier density and mobility reached at 1.1×10¹⁹ cm⁻³ and 4.8 cm²/V s, respectively. Si still acted as a shallow donor even for the heavily doped Al_0.6Ga_0.4N.     

Arsenic cluster superlattice in gallium arsenide grown by low-temperature molecular-beam epitaxy

Molecular-beam epitaxy at 200 °C is used to grow an InAs/GaAs superlattice containing 30 InAs delta-layers with a nominal thickness of 1 monolayer, separated by GaAs layers of thickness 30 nm. It is found that the excess arsenic concentration in such a superlattice is 0.9×10²⁰ cm⁻³. Annealing the samples at 500 and 600 °C for 15 min leads to precipitation of the excess arsenic mainly into the InAs delta-layers. As a result, a superlattice of two-dimensional sheets of nanoscale arsenic clusters, which coincides with the superlattice of the InAs delta-layers in the GaAs matrix, is obtained. Fiz. Tekh. Poluprovodn. 32, 1161–1164 (October 1998)     

Metal-organic vapour-phase epitaxy of gallium nitride nanostructures for optoelectronic applications

The two main topics with respect to better gallium nitride (GaN)-based optoelectronic device performance are the improvement of crystal quality and of light extraction. Concerning the first topic, the epitaxial growth of GaN-related materials has to be improved. Since native substrates with good quality are still expensive, foreign substrates like sapphire or silicon which are much cheaper are used, but they introduce a lattice as well as a thermal mismatch leading to detrimental crystal defects. Several approaches to reduce the defect density exist, but in most cases they are coupled with a much higher technological effort.We present an alternative solution to decrease the defect density by the growth of GaN nanostructures, where the small footprint and high aspect ratio leads to a much lower influence of the substrate. Metal-organic vapour-phase epitaxy of GaN nanostructures and InGaN/GaN multi-quantum wells was carried out in a vertical reactor with close-coupled showerhead. Studies on the morphologic properties have been carried out by scanning electron microscopy and energy-dispersive X-ray spectroscopy to reveal the influence of growth parameters and material composition. Cathodoluminescence measurements show the good optical properties of the GaN as well as of the InGaN/GaN structures.     

Reactive ion etching of gallium nitride films

Reactive ion etching (RIE) was performed on gallium nitride (GaN) films grown by electron cyclotron resonance (ECR) plasma assisted molecular beam epitaxy (MBE). Etching was carried out using trifluoromethane (CHF₃) and chloropentafluoroethane (C₂ClF₅) plasmas with Ar gas. A conventional rf plasma discharge RIE system without ECR or Ar ion gun was used. The effects of chamber pressure, plasma power, and gas flow rate on the etch rates were investigated. The etch rate increased linearly with the ratio of plasma power to chamber pressure. The etching rate varied between 60 and 500Å/min, with plasma power of 100 to 500W, chamber pressure of 60 to 300 mTorr, and gas flow rate of 20 to 50 seem. Single crystalline GaN films on sapphire showed a slightly lower etch rate than domain-structured GaN films on GaAs. The surface morphology quality after etching was examined by atomic force microscopy and scanning electron microscopy.     

Improving the functional characteristics of gallium nitride during vapor phase epitaxy

The mechanisms of gallium nitride crystallization during vapor phase epitaxy are theoretically analyzed. The limited growth in the boundary layer is thoroughly investigated. The conditions for control of the process and intensification of the mass transfer are determined. The effect of the substrate rotation speed on the crystallization mechanism is experimentally studied.     

The use of magnesium to dope gallium nitride obtained by molecular-beam epitaxy from activated nitrogen

A kinetic model for doping gallium nitride with magnesium in the course of molecular-beam epitaxy from plasma-activated nitrogen is suggested; the model parameters are determined. The theory relies on competitive quasi-equilibrium incorporation of Mg and Ga into the Group III sublattice and accounts for the main observed special features of doping, specifically, the dependence of Mg incorporation on temperature and on the V/III ratio in the incident fluxes.     

Properties of manganese-doped gallium arsenide layers grown by liquid-phase epitaxy from a bismuth melt

The electrical and photoluminescence properties of p-GaAs: Mn(100) layers grown by liquid-phase epitaxy from a bismuth solvent at various temperatures are investigated. It is shown that such layers have a low concentration of background impurities and a low degree of electrical compensation up to a hole concentration of p=1×10¹⁸ cm⁻³ at 295 K. As the concentration of manganese in the liquid phase increases, the concentration of donors in the GaAs: Mn layers increases superlinearly, while the concentration of ionized acceptors increases sublinearly. This leads to an increase in the compensation factor. The donor and acceptor concentrations, as well as the degree of compensation, increase more slowly with increasing temperature. Reasons for the donor compensation are discussed from a crystal-chemical point of view, and it is shown that the preassociation of manganese and arsenic atoms in the liquid phase could be responsible for generating these compensated donors. It is postulated that the compensating donors are nonradiative recombination centers, whose concentration increases with increasing doping level more rapidly than does the concentration of Mn_Ga acceptors. Fiz. Tekh. Poluprovodn. 32, 791–798 (July 1998)     

Intrinsic defect states in PbTe single-crystal films grown by laser-modulated epitaxy

The electrical properties of PbTe/KCl(KBr) layers grown by infrared-laser-modulated epitaxy and their dependences on conditions of fabrication (power density of the laser beam W, substrate temperature T _s ) have been investigated. It is established that the R _H (T) dependences can be explained within the framework of a two-level model in which one of the levels (E _d1) is in the conduction band and the second level E _d2 is in the band gap. The positions of the energy levels and their density of states depend on the conditions of growth. Fiz. Tekh. Poluprovodn. 32, 47–49 (January 1998)     

Ferromagnetic-resonance linewidth of thick yttrium?iron-garnet films grown by liquid-phase epitaxy

Films of yttrium?iron garnet have been grown on gadolinium-gallium-garnet substrates by liquid-phase epitaxy with thickness up to 100 ?m. Measurements by the bandstop-filter technique in the frequency range 2?8 GHz have shown resonance line-widths as low as 20 A/m(0.25 Oe). These results are compared with measurements of linewidth by the cavity-resonance technique at 9.5 GHz.     

The scanning tunneling microscopy and spectroscopy of GaSb1-xBix films of a few-nanometer thickness grown by molecular beam epitaxy

The ultrahigh vacuum scanning tunneling microscope (STM) was used to characterize the GaSb1-xBix films of a few nanometers thickness grown by the molecular beam epitaxy (MBE) on the GaSb buffer layer of 100 nm with the GaSb (100) sub-strates.The thickness of the GaSb1-xBix layers of the samples are 5 and 10 nm,respectively.For comparison,the GaSb buffer was also characterized and its STM image displays terraces whose surfaces are basically atomically flat and their roughness is generally less than 1 monolayer (ML).The surface of 5 nm GaSb1-xBix film reserves the same terraced morphology as the buffer layer.In contrast,the morphology of the 10 nm GaSb1-xBix film changes to the mound-like island structures with a height of a few MLs.The result implies the growth mode transition from the two-dimensional mode as displayed by the 5 nm film to the Stranski-Krastinov mode as displayed by the 10 nm film.The statistical analysis with the scanning tunneling spectroscopy (STS)measurements indicates that both the incorporation and the inhomogeneity of Bi atoms increase with the thickness of the GaSb1-xBix layer.     

Indium gallium arsenide antimonide photodetector grown by liquid phase epitaxy: Electrical characterization and optical response

Current–voltage (I–V) and R₀A curves and spectral response as a function of bias voltage and temperature of p–n indium gallium arsenide antimonide (In_0.14Ga_0.86As_0.13Sb_0.87)/n-GaSb photodiodes are presented. InGaAsSb quaternary alloys with a bandgap energy of about 653 meV were grown using the liquid phase epitaxy technique on top of (100) GaSb substrates. Device structure was fabricated using a process that includes passivation with sodium sulfide, thermal annealing and metallizations. The diode architecture was a back-illuminated (B-I) structure with a ring-shaped metallic contact in the GaSb substrate face. Photodiode spectral response showed good performance in the entire temperature range between 20 K and 300 K.     

Controlled oxygen incorporation in indium gallium arsenide and indium phosphide grown by metalorganic vapor phase epitaxy

The defect engineering in metalorganic vapor phase epitaxy In_xGa_1-xAs and InP by controlled oxygen doping using diethyl aluminum ethoxide (DEALO) was developed in this study. DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in In_xGa_1−xAs: Si with 0 ≤ x ≤ 0.25. With the same DEALO mole fraction during growth, the incorporation of Al and O was found to be independent of x, but the compensation of Si donors decreases with increasing In content. Deep level transient spectroscopy analysis on a series of In_xGa_1-xAs: Si. samples with 0 ≤ x ≤ 0.18 revealed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. As the In composition was increased, one or more of these deep levels became resonant with the conduction band and led to a high electron concentration in oxygen doped In_0.53Ga_0.47As. Low temperature photoluminescence emission measurements at 12K on the same set of samples revealed the quenching of the near-band edge peak, and the appearance of new oxygen-induced emission features. DEALO doping in InP has also led to the incorporation of Al and O, and the compensation of Si donors due to oxygen-induced multiple deep levels.     

Structure of GaN films grown by molecular beam epitaxy on (0001) sapphire

GaN films grown by electron-cyclotron resonance plasma-assisted molecular beam epitaxy were studied by transmission electron microscopy and x-ray diffraction (XRD). Two sets of films were compared that were grown under identical conditions except for the ratio of the Ga to N flux. Films with a 30% higher Ga to N ratio (A films) were found to contain inversion domains (IDs). No IDs were found in films grown with a lower Ga to N ratio (B films), but instead the zinc-blende GaN was found near the film substrate interface. A narrower XRD rocking curve width along the (0002) direction and a broader rocking curve width along the asymmetric (1102) axis were found for A films compared to B films.     

Electrical and optical properties of CdHgTe films grown by molecular-beam epitaxy on silicon substrates

The electrical and optical properties of epitaxial CdHgTe films grown on silicon substrates by molecular-beam epitaxy have been studied. The results of photoluminescence measurements are indicative of the high structural perfection of the films, and Hall data combined with low-energy ion treatment point to a low concentration of residual donors (??5 × 10¹⁴ cm^?3). Acceptor states supposedly related to the capture of impurities at structural defects typical of strongly lattice-mismatched heteroepitaxial structures are found in the films.     

Characterizations of GaN films grown with indium surfactant by RF-plasma assisted molecular beam epitaxy

A small indium flux was used as a surfactant during the growth of gallium nitride by rf-plasma assisted molecular beam epitaxy. The effects of the In surfactant on the optical and structural properties of undoped GaN were studied by photoluminescence (PL), X-ray diffraction, atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). PL studies show that the use of In surfactant is beneficial to the reduction of deep-level defects. The X-ray rocking curves demonstrate a 20% decrease in the full width at half maximum value for the films grown with In surfactant. AFM studies show that the root mean squared surface roughness for films grown with and without In surfactant are 5.86 and 6.99 nm respectively indicating significant improvement in surface morphology. The improved surface morphology is attributed to the enhanced 2-dimensional growth promoted by the application of In surfactant. RBS studies show that the χ_min values along [0 0 0 1] direction are 2.06% and 2.16% for the samples grown with and without In surfactant respectively. Off-normal ion channeling studies were performed to further investigate the effects of In surfactant on the crystallinity. It is found that the number density of stacking faults is smaller for the sample grown with In surfactant compared to the one grown without In surfactant. However, defect analysis shows that dislocations are found in the sample grown with In surfactant in contrary to the one grown without In surfactant. We speculate that there is a thickness limit of GaN grown with In surfactant and the thickness of our samples exceed this limit, leading to the presence of dislocation.