Metalorganic Vapor Phase Epitaxy System Research Articles

Growth of self-assembled nanosize InGaN/GaN multiple quantum wells embedded in amorphous SiN x by metalorganic vapor phase epitaxy

We report on the growth and photoluminescence of InGaN/GaN multiple quantum wells (MQWs) grown on GaN nanocrystals embedded in amorphous SiN x , grown on a p-type Si(1 0 0) substrate. p-Type Si(1 0 0) was thermally nitridated using NH 3 to form an amorphous SiN x layer in a metalorganic vapor phase epitaxy system. GaN nanocrystals were then grown on the SiN x layer, followed by the growth of InGaN/GaN MQWs on the GaN nanocrystals. These nanosize MQWs were capped with amorphous SiN x in a plasma enhanced chemical vapor deposition system. The findings show that nanosize InGaN/GaN MQWs can be embedded in amorphous SiN x grown on p-type Si(1 0 0) and that these self-assembled nanostructures may be used as new nanosize light-emitting sources as evidenced by photoluminescence from nanosize MQWs.

Real-Time Observation of Electron-Beam Induced Mass Transport in Strained InGaAs/AlGaAs Layers on GaAs (100) and (311)B Substrates

We have studied surface deformation due to electron-beam irradiation in strained InGaAs/AlGaAs layers grown on GaAs (100) and (311)B planes in a horizontal low-pressure metalorganic vapor phase epitaxy system at about 800°C. The surface deformation was observed in real time using a high-resolution scanning electron microscope at a magnification of 300,000. The surface deformation occurred from the inside of InGaAs/AlGaAs grown layer under the electron-beam irradiated area with the accelerating voltage of 30 kV and the scanning time ranging from 60 to 120 s. The surface deformation was not consist of amorphous-carbon contamination. The mass transport seems to be caused by the residual strain relaxation due to electron-beam irradiation.

In situ thermal nitridation of GaAs using metalorganic vapor phase epitaxy

The in situ thermal nitridation of GaAs surfaces has been performed by annealing GaAs in an ammonia ambient within a metalorganic vapor phase epitaxy (MOVPE) system. The shift of the GaAs surface Fermi level, and hence the surface charge density, resulting from the in situ thermal nitridation has been studied using photoreflectance (PR) spectroscopy. Samples consisting of an undoped GaAs layer on highly doped n-GaAs (UN +) and p-GaAs (UP +) structures allow for the determination of the surface Fermi level position. These structures were grown by MOVPE and in situ thermal nitridation was performed after growth within the MOVPE system without exposure to air. After nitridation, the surface Fermi level can be shifted by ∼0.23 eV towards the conduction band edge for UN + structures and by ∼0.11 eV towards the valence band edge for UP + structures from the normally mid-gap `pinned' positions. The surface morphology of nitrided surfaces was determined by atomic force microscopy (AFM).

Monomethylsilane as a New Dopant Precursor for n-Type GaN Grown by MOVPE

Monomethylsilane (MMSi) is demonstrated as an alternative Si dopant precursor for silane. It is stable in the air and it is in gas phase at room temperature. Si-doped GaN films were grown by metalorganic vapor-phase epitaxy (MOVPE) using MMSi. The electron concentration was controlled linearly with the MMSi flow rate in the range 1 x 10{sup 18} cm{sup -3} to 2 x 10{sup 19} cm{sup -3}. Carbon contamination in the n-type GaN was measured by secondary ion mass spectroscopy (SIMS) and was lower than the detection limit of SIMS (1 x 10{sup 17} cm{sup -3}). The electron mobility was equal to or higher than those obtained from other reported dopant precursors for a given electron concentration. These results indicate that it is a suitable dopant precursor to obtain n-type GaN in high quality and a much safer MOVPE system can be established. (orig.) 6 refs.

MOVPE of ZnMgSSe heterostructures for optically pumped blue-green lasers

We report on the growth of ZnMgSSe/ZnSSe/ZnSe heterostructures in a low pressure metalorganic vapor phase epitaxy (MOVPE) system at 400 hPa and a growth temperature of 330°C. The precursor combination was dimethylzinc(triethylamine adduct), ditertiarybutylselenium, ditertiarybutylsulphur, and bismethylcyclopentadienylmagnesium. This combination allows the reproducible adjustment of the alloy composition in a wide range (currently up to 40% S and 32% Mg) maintaining high crystal homogeneity and almost lattice matched growth. Undoped separate confinement heterostructure (SCH) lasers with ZnMgSSe cladding and ZnSSe guiding layers were deposited on GaAs substrates. X-ray diffraction (reciprocal space mapping), photoluminescence (PL) at 14–300K, PL excitation, and optical pumping experiments were performed. The quantum wells show a high luminescence efficiency up to room temperature. Optical pumping experiments were carried out at various temperatures (77, 300–375K) and excitation densities using a nitrogen laser. The lasing threshold could be determined to be less than 20 kW/cm2 at 77K, and even room temperature lasing was observed at an excitation density which was below 200 kW/cm2.

MOVPE-grown millimeter-wave InGaAs mixer diode technology and characteristics

The merits of InGaAs-based millimeter-wave mixer diodes are explored experimentally and theoretically. Schottky junctions on InGaAs exhibit barriers (/spl phi//sub b/) in the neighborhood of 0.25 eV. The high mobility of InGaAs contributes to the low n/sup +/ sheet resistances of 1.9-5 /spl Omega//square for 1-/spl mu/m n/sup +/ InGaAs layers (n/sub s/=1.5/spl times/10/sup 19/ cm/sup -3/, /spl mu//sub n/=1800 cm/sup 2//V/spl middot/s) grown with our in-house Metalorganic Vapor Phase Epitaxy (MOVPE) system, The design, material growth, fabrication, and characterization of InGaAs integrated mixer/antennae are reported. Pt plating technology, adapted here for InGaAs Schottky contacts, has improved the ideality factor (/spl eta/) and yield relative to conventional evaporated Pt. With 810 /spl mu/W of local oscillator power, applied to the diode, and zero DC bias, an integrated InGaAs mixer/antenna demonstrated an excellent diode performance of 199 K RF input double-sideband noise temperature with a corresponding single-sideband (SSB) conversion loss (L/sub c/) of 5.0 dB at LO, RF, and IF frequencies of 94 GHz, 94 GHz/spl plusmn/1.4 GHz, and 1.4 GHz, respectively. Likewise, the diodes in an InGaAs subharmonic integrated mixer/antenna demonstrated an equivalent RF-port double-sideband (DSB) noise temperature (T/sub mix/) of 1058 K and single-sideband conversion loss of 10.2 dB at 180 GHz with a 90-GHz LO power (PLO) of 1.6 mW. Compared to GaAs diodes with RF coupling and IF losses removed, the single-ended InGaAs noise temperature results were within 46-100 K of those for state-of-the-art GaAs mixer diodes while requiring significantly less LO power.

Observation of the 2D–3D growth mode transition in the system

Self-organized InAs quantum dot structures were prepared by low pressure metalorganic vapor phase epitaxy (MOVPE) using the Stranski-Krastanow growth mode. We present photoluminescence (PL) and atomic force microscopy (AFM) studies of the transition from a 2D InAs wetting layer to 3D quantum sized islands. The very narrow window where this transition takes place could be studied in detail by taking advantage of the slight growth rate gradient of our MOVPE system. After the growth of a critical layer thickness, first quantum dots occur. From the PL spectra obtained at different positions on the wafer, we conclude that a part of the wetting layer is consumed by the dot formation process. This is further confirmed by AFM measurements. Also a qualitative correlation between dot density and PL intensity is described. Moreover, we observed that the dot formation can be suppressed by instantaneous overgrowth. Besides the overgrowth temperature the growth interruption between the InAs film and the GaAs cap layer was found to be of great importance for the dot formation.

Influence of lattice relaxation on the properties of [formula omitted] single quantum wells by MOVPE

The growth of ZnSeZnS single quantum well (SQW) structures was performed by atomic layer epitaxy (ALE) in an atmospheric pressure metalorganic vapour phase epitaxy (MOVPE) system. Through the photoluminescence measurement of ZnSeZnS SQWs, we observed clear shifts of the excitons to higher energies with decreasing well width, which demonstrate effects of strain and quantum confinement. Transition energies were calculated considering (i) a simple square well potential and (ii) a parabolic potential model under the action of strain effects. From comparison of the exciton energy with the calculated transition energies, we conclude that lattice relaxation induced interdiffusion occurs as the well width becomes thicker than the critical thickness.

III-V Nitride Growth by Atmospheric-Pressure MOVPE with a Three-Layered Flow Channel

ABSTRACTWe introduce III-V nitrides growth including GaN as well as InGaN by a newly developed atmospheric-pressure metal-organic vapor phase epitaxy system with a three layered flow channel which is a promising system for a large scale production. First, we have shown through computer simulation that a laminar flow of gases is maintained at 1000 °C in the three layered flow channel. Second, as a part of epitaxial results, we have found that the surface roughness of a low temperature-grown buffer layer on sapphire substrates, which can be measured by atomic force microscope, should be minimum in order to grow high quality GaN. We also report the growth of a double heterostructure of Ino. 15Gao.85N/GaN which shows a strong near band-edge emission in room temperature photoluminescence.

Evolution of surface topography during metalorganic vapor phase epitaxy of AlxGa1−xAs (0 ≦x ≦ 1)

The evolution of surface topography during epitaxial growth of AlxGa1−xAs (0 ≦ x ≦ 1) is observed using angle-resolved elastic light scattering within a metalorganic vapor phase epitaxy system. The density and orientation of extended topographical features are monitored during various growth phases: annealing, initiation, steady state, and conclusion. Transient monolayer oscillations and persistent fluctuations in surface roughness are observed. Also shown are the emergence of [011] oriented B-steps and the dependence of the topography upon V/III ratio.

ZnMgSSe/ZnSSe/ZnSe-heterostructures grown by metalorganic vapor phase epitaxy

ZnMgSSe heterostructures have been grown in a low-pressure metalorganic vapor phase epitaxy system with the precursors dimethylzinc triethylamine, ditertiarybutylselenide, tertiarybutylthiol, and biscyclopentadienylmagnesium at 330°C and a total pressure of 400 hPa. The optimization of the single layers was carried out by means of low temperature photoluminescence. Only the near band edge emission was observable with negligible deep levels. The heterostructures consisting of a triple ZnSe quantum well showed intense luminescence which hints at an effective carrier confinement. Scanning transmission electron microscopy investigations of the heterostructures still showed structural detects since the layers were not lattice matched to the GaAs substrate yet.

Monitoring of gas-phase species in metalorganic vapor phase epitaxy by fiber-optics based Fourier transform infrared spectroscopy

Fiber-optics based Fourier transform infrared (FTIR) spectroscopy is demonstrated as a technique for remote in-situ monitoring of concentration levels of organometallic species in gas delivery lines to metalorganic vapor phase epitaxy (MOVPE) systems. The concentration measurements are based on infrared absorption at 2800–3000 cm -1 corresponding to C-H stretching vibrations in alkyl ligands. Trimethylgallium (TMG), trimethylindium (TMI), tertiary butyl phosphine (TBP), and tris-dimethylaminophosphine (DMAP) are used in sample monitoring studies. The detection limit varies with the number of C-H bonds from 0.05 Torr at room temperature for TMG and TMI, to 0.006 Torr for DMAP. The ability of the technique to detect chemical species, as well as to monitor concentration levels, is illustrated by the appearance of methane in turn-on transients of TMG and TMI bubblers that have been stored for a length of time. A mathematical analysis of turning on and off low from a bubbler containing an organometallic precursor is presented and used to identify wall condensation and chemical interactions for TMI and DMAP in gas delivery lines.

Novel technique for p-type nitrogen doped ZnSe epitaxial layers

We report a novel technique to obtain p-type ZnSe layers doped with nitrogen. The layers were grown in a low-pressure metalorganic vapor phase epitaxy system using ammonia as the dopant source. A rapid thermal anneal was used to enhance the activation of the nitrogen acceptors. Net acceptor concentration values as high as 3×1016/cm3 were obtained from capacitance-voltage measurements and the profile was uniform over the thickness of the epitaxial layers. The 7 K photoluminescence spectrum was dominated by the acceptor bound exciton peak; the donor-acceptor pair spectra were also observed.

Characterization of AlGaP/GaP heterostructures grown by MOVPE

High quality Al x Ga 1- x P/GaP heteroepitaxial layers were grown by a barrel-type multiwafer metalorganic vapor phase epitaxy system. Fundamental aspects concerning the growth and the heterostructures, such as distribution coefficient of Al, critical layer thickness, doping properties, and band discontinuities at the heterojunctions, have been investigated.

The growth of GaAs, AlGaAs, and selectively doped AlGaAs/GaAs heterostructures by metalorganic vapor phase epitaxy using tertiarybutylarsine

The prevention of disastrous leakage of AsH3 is a requirement for metalorganic vapor phase epitaxy systems. Less hazardous organoarsine has been investigated as an alternative to AsH3 , and recently, tertiarybutylarsine (tBAs) has been used as an arsenic source. So far the use of tBAs has been restricted to fundamental experiments. The growth of GaAs, AlGaAs, and selectively doped AlGaAs/GaAs heterostructures has been studied using tBAs and AsH3, and the properties of the epilayers grown using both sources have been compared. From the PL spectra at 4.2 K, it was determined that GaAs films using tBAs were of high purity and equivalent to those using AsH3. The properties of AlGaAs grown using tBAs are as good as those using AsH3. A higher V/III ratio results in high-quality AlGaAs layers. The epitaxial uniformity of growth rate and AlAs mole fraction along a wafer using tBAs was poorer than those using AsH3 due to vapor phase reactions in the trimethylgallium-tBAs mixture. However, the increase of total gas flow rate in the reactor has the effect of improving uniformity. The activation efficiency of Si in AlGaAs is the same for both sources. The properties of heterostructures grown using tBAs are similar to those using AsH3. The sheet carrier concentration and electron mobility at 77 K with a spacer layer thickness of 35 Å were 9.5×1011 cm−2 and 48 000 cm2 V−1 s−1, respectively. This suggests that tBAs can be used as an alternative to AsH3, for growing device-quality GaAs and AlGaAs.

InP (and GaAs) substrate stabilization by the presence of GaAs (and InP) in a metal-organic vapour-phase epitaxy system

Metal-organic vapour-phase epitaxy (MOVPE) is a well-established technique for semiconductor growth. Like molecular-beam epitaxy, liquid-phase epitaxy, and vapour-phase epitaxy, it requires a stabilized substrate surface prior to growth to obtain a high-quality crystal. Studies of the stabilization of GaAs and InP substrates placed side by side with their interactions under V-hydride flows can provide valuable information. Here we show the effect of exposing GaAs and InP substrates to AsH3 and (or) PH3 in the temperature range from 550 °C to 750 °C, in an MOVPE reactor. The presence of a GaAs substrate partially stabilizes the InP substrate; the stabilized area decreases when either temperature of AsH3 flow increases. The presence of a stabilized InP substrate (under PH3 flow) also partially stabilizes the GaAs substrate. Surface analysis shows that the stabilized area contains column-V species coming from the neighbouring substrate. These column-V species are competing with species originating from the V hydrides (AsH3 or PH3). From the analysis of these experiments, we conclude that the V-hydride species active in the MOVPE environment are not dimers or tetramers. Annealing the substrates under both AsH3, and PH3 shows preference for As-specics aggregation at the substrate surface. The simple model previously used to prediet stabilization is extended to cover this mixed-hydride situation.

Low temperature growth of GaN single crystal films using electron cyclotron resonance plasma excited metalorganic vapor phase epitaxy

A novel low-temperature-growth technique for GaN single crystal films has been developed utilizing electron cyclotron resonance (ECR) plasma excitation. The GaN film is grown in a low pressure metalorganic vapor phase epitaxy (MOVPE) system employing the reaction of trimethylgallium (TMG) with highly activated nitrogen produced by ECR excitation of ammonia. Using this ECR excitation technique, GaN single crystal films are grown on a sapphire basal plane at low substrate temperatures from 300 to 400° C under a molar ratio of NH 3 to TMG of 100 and a growth pressure of 2 × 10 −4 Torr. Furthermore, Zn-doped GaN single crystal films are successfully grown by adding dimethylzinc. The surface morphology of the GaN film is very smooth and the electrical properties of the undoped film are comparable to those with a MOVPE technique at high growth temperatures. Photoluminescence experiments at room temperature reveal that a blue luminescence peak appears in Zn-doped GaN and that the peak shifts to longer wavelengths with increases in the Zn-doping level.

Growth of GaN single crystal films using electron cyclotron resonance plasma excited metalorganic vapor phase epitaxy

A low-temperature growth technique for GaN single crystal films has been developed utilizing electron cyclotron resonance (ECR) plasma excitation. The GaN film has been grown in a low pressure metalorganic vapor phase epitaxy (MOVPE) system using the reaction of trimethylgallium with highly activated nitrogen extracted from the ECR plasma chamber. Growth conditions of GaN single crystal films have been clarified by examining reflection high-energy electron diffraction patterns. The surface morphology of the GaN single crystal film is very smooth and electrical properties are comparable to those of a MOVPE technique at high growth temperatures.