Metalorganic Vapor Phase Epitaxy Growth Research Articles

Wavelength demultiplexer using GaInAs-InP MQW-based variable refractive-index arrayed waveguides fabricated by selective MOVPE

A GaInAs-InP multiple quantum well (MQW)-based wavelength demultiplexer composed of an arrayed waveguide in which the refractive index varies across the array was fabricated. Since optical path length differences between waveguides in the array are achieved through refractive-index differences that are controlled by SiO/sub 2/ mask design in selective metal-organic vapor phase epitaxy (MOVPE), straight waveguide gratings having reduced optical propagation losses can be achieved. Furthermore, by employing MQW waveguides, variations in the refractive index may be induced through an applied electric field, allowing the device to manipulate wavelengths dynamically. A straight arrayed waveguide device having a 1.4% difference in refractive index was fabricated using an asymmetric side mask via a single selective MOVPE growth. The achievement of a diffraction angle difference of 4.40/spl deg/ between wavelengths of 1520 and 1580 nm was confirmed experimentally. In addition, a preliminary wavelength demultiplexer with a wavelength separation of approximately 25 nm and a free spectral range (FSR) of approximately 100 nm was also fabricated.

Growth mechanism and structural characterization of hexagonal GaN films grown on cubic GaN (1 1 1)/GaAs (1 1 1)B substrates by MOVPE

Hexagonal phase GaN layers were grown by metalorganic vapor phase epitaxy (MOVPE) on GaAs (1 1 1)B substrates using the cubic phase GaN (c-GaN) as an intermediate layer. High-resolution X-ray diffraction (HRXRD) and transmission electron microscopy (TEM) measurements showed fairly good crystalline qualities of the h-GaN layers. Dislocation densities estimated from cross-sectional TEM micrographs were found to be as low as 10 7–10 8 cm −2. Flat growth of the c-GaN intermediate layer on GaAs (1 1 1)B substrate was achieved at a low-growth temperature (600 °C). The interface between the GaN layer and the GaAs (1 1 1)B substrate is very smooth without any voids, in spite of the high-growth temperatures of 880–960 °C. It is interesting that the lattice-matched h-GaN layer to the c-GaN intermediate layer can be obtained by controlling the cubic-to-hexagonal structural transition during the MOVPE growth process at appropriate growth temperatures. The growth mechanism and characteristics of the grown h-GaN layers are discussed.

Effect of thermal radiation and absorption in GaN-MOVPE growth modeling on temperature distribution and chemical state

The effect of radiative heat transfer in metalorganic vapor-phase epitaxial growth of GaN on temperature distribution and chemical state was studied. We compared numerical simulations performed by using four kinds of models for the quartz absorptivity, transmissivity and reflectivity. The models are a transparent-body model, a blackbody model and two models using the experimental data measured at room temperature and at 1073 K by Fourier transform infrared spectroscopy. Numerical simulation using these models exhibited different results in temperature and chemical states, indicating that absorption of the quartz optical property at the elevated temperature is important to calculate accurate temperature field and chemical reactions.

MOVPE growth and optical investigations of InGaPN alloys

InGaPN alloy films were grown on GaP (0 0 1) substrates by metalorganic vapor phase epitaxy (MOVPE) at 635 °C using trimethylgallium (TMGa), trimethylindium (TMIn), PH 3 and 1,1-dimethylhydrazine (DMHy) as the precursors of Ga, In, P and N, respectively. For the fixed combination of TMGa, PH 3 and TMIn flows, the composition control of In x Ga 1− x P 1− y N y was achieved simply by changing the molar flow ratio of DMHy to the total group V sources, giving y=0–8.7% and x=17.6%. The grown films show a systematic red shift of the photoluminescence (PL) peak energy with increasing N content. On the other hand, with increasing the TMIn molar flow while the other flows were fixed, the N incorporation is much affected by the TMIn flow due to some reaction kinetics. In fact, the N content was decreased from y=2.6% to 1.6% while the In content was increased from x=0 to 10.9%. As a result, the apparent blueshift of the PL peak energy for this growth series is due to the reduction of N incorporation with increasing TMIn flow. The lattice-matched In x Ga 1− x P 1− y N y ( x=17.6%, y=7.4%) film showed an excellent structural and optical quality in spite of the relatively high N content.

High-power and high-temperature operation of Mg-doped AlGaInP-based red laser diodes

This paper reports on high-power and high-temperature operation of an AlGaInP-based high-power red laser diode with magnesium (Mg)-doped quaternary-alloy cladding layer. The use of Mg dopant with small diffusion coefficient enables abrupt doping profiles as well as high carrier concentrations when compared to conventional zinc (Zn) dopant. It was also found that the metal-organic vapor phase epitaxial (MOVPE) growth of Mg-doped quaternary AlGaInP alloy is not affected by so-called reactor memory effects, while unintentional incorporation of Mg is observed in GaAs after the growth of Mg-doped GaAs layers. The higher carrier concentration in the p-type cladding layer enhanced carrier confinement in the active layer so that device performance at high temperature is improved. The abrupt doping profile suppressing dopant diffusion into the active layer eliminates the nonradiative recombination in the active layer resulting in higher external quantum efficiency. The characteristic temperature of the Mg-doped red laser with a lasing wavelength of 659 nm is as high as 167 K while the Zn-doped laser exhibits a temperature of 127 K. High kink-free output power of 150 mW is achieved at 75/spl deg/C.

Fabrication and characterization of GaAs two-dimensional air-hole arrays on GaAs (1 1 1)A substrates using selective-area MOVPE

We report on the selective-area metal-organic vapor-phase epitaxial (SA-MOVPE) growth of GaAs-based periodic air-hole arrays on partially masked GaAs (1 1 1)A substrates for application to two-dimensional photonic crystals (2D PhCs). We obtained uniform 1-μm-pitch GaAs 2D air-hole arrays on GaAs (1 1 1)A substrates with vertical side walls under high AsH 3 partial pressure and low-growth-rate conditions. However, under these growth conditions, lateral over-growth (LOG) occurs at three corners of hexagonal air-hole, and the hole shape change to triangle. We clarified the mechanism of selective area growth on a GaAs (1 1 1)A substrates. We also tried shorter pitch (400 nm) GaAs air-hole arrays and AlGaAs SA-MOVPE on GaAs (1 1 1)A.

Fabrication of InAs quantum dots on InP(100) by metalorganic vapor-phase epitaxy for 1.55 μm optical device applications

A change in the density and wavelength of InAs quantum dots (QDs) on InGaAsP/InP(100) substrate grown by metalorganic vapor-phase epitaxy (MOVPE) in accordance with variation in the growth conditions was studied, aiming at optical device applications in the 1.55 μm region. In the moderate V/III ratio region, the size of QDs was found to decrease while the density increased as the group-V source was reduced, but on the other hand, both of them increased monotonously with increasing InAs supply. The combination of changing the V/III ratio and InAs supply allowed us to control the density and wavelength of QDs independently so that QDs with a density as high as 5.6×1010 and a 1.6 μm emission were obtained. The letter reports the MOVPE growth technique of QDs on InGaAsP/InP(100), which connects QDs with mature 1.55 μm device technology.

Specific structural and compositional properties of (GaIn)(NAs) and their influence on optoelectronic device performance

We have grown (GaIn)(NAs) lattice-matched bulk as well as compressively strained multi-quantum-well structures by metal-organic vapour-phase epitaxy (MOVPE) suitable for either solar cell or laser applications, respectively. By applying a specific novel TEM dark-field technique columnar strain fields, which are possibly caused by chain-like N ordering in the samples, have been detected. Valence force field calculations show that indeed these chains are energetically stable in Ga(NAs). This chain-like ordering can be dissolved in (GaIn)(NAs), however, upon appropriate annealing, as verified experimentally. On the other hand we find that device performance especially of lasers is limited by carbon impurities in the active (GaIn)(NAs) region of the lasers. The strong affinity of N–C results in an enhanced incorporation of C if the N content in the material is increased. The paper also shows the sources of C incorporation in (GaIn)(NAs) MOVPE growth and how its incorporation can possibly be avoided.

MOVPE growth experiments of the novel (GaIn)(NP)/GaP material system

Highly compressively strained (GaIn)(NP) quantum wells have been grown on (1 0 0) GaP substrates by metal organic vapour-phase epitaxy (MOVPE). We achieve a high structural quality of the grown multiple quantum well structures for this novel, metastable material system. Competition between the group-V elements on the surface determines the N incorporation in Ga(NP) as well as (GaIn)(NP). For the ternary material system Ga(NP) the N content of the deposited layers does not depend on the growth rate in contrast to the quaternary system (GaIn)(NP), where the N incorporation is enhanced with increasing growth rate. This suggests a desorption controlled N incorporation process for the In-containing material. This is in accordance with the strong dependence of the N content in the material from the growth temperature and the In content. In addition — due to the metastability of the material systems under investigation — the maximal achievable N content in Ga(NP) and (GaIn)(NP) is limited when good crystal quality is to be retained.

Growth and characterization of p-type InGaAs on InP substrates by LP-MOVPE using a new carbon-dopant source, CBrCl 3

Low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE) growth of lattice-matched p-type InGaAs on InP substrates using a new dopant precursor, carbon trichloro bromide (CBrCl 3), has been investigated. The p-type conductivity with a hole concentration up to 10 19 cm −3 based on the Hall measurement has been achieved only in the samples grown under very limited conditions such as a V/III ratio below 5, a growth temperature around 540 to 550 °C and high growth rates over 100 nm/min. The X-ray rocking-curve analysis of these samples has revealed that the conduction type does not depend on the type of stress such as tensile or compression caused by a very small lattice mismatch within |Δ a|⩽5×10 −3. However, it has been found that samples with hole concentration over 10 18 cm −3 always exhibit the tensile stress and the efficiency of the p-type doping has been enhanced by the introduction of tensile stress controlled by the growth.

C-doped GaAsSb base HBT without hydrogen passivation grown by MOVPE

Hydrogen passivation of C-doped GaAsSb during both metal-organic vapor phase epitaxy growth and annealing under hydride atmosphere was investigated in detail. It is well known that C accepters are easily passivated by hydrogen in III-V materials. We have found that hardly any hydrogen atoms are incorporated into C-doped GaAsSb if the annealing is performed under a hydride atmosphere. We have also found that AsH 3 exposure yields a lower rate of hydrogen passivation of the C-doped GaAsSb than during C-doped GaAsSb growth. These results are very advantageous for fabricating C-doped GaAsSb base heterojunction bipolar transistors (HBTs) without hydrogen passivation. In fact, we have successfully fabricated an InP/GaAsSb/InP D-HBT whose hydrogen concentration in the base ([C]: 8×10 19 cm −3, thickness: 20 nm) was under the detection limit of our SIMS measurement equipment. We demonstrate a relatively high-performance HBT ( β∼40, f T∼300 GHz, f max∼200 GHz, and BV CEO∼6 V) without any dehydrogenation process.

Correlation of film properties and reduced impurity concentrations in sources for III/V-MOVPE using high-purity trimethylindium and tertiarybutylphosphine

Trimethylindium (TMI) and tertiarybutylphosphine (TBP) are an attractive combination of sources for Metalorganic vapor phase epitaxy (MOVPE) of InP-based compounds. TBP is used to deposit high-quality layers at significantly lower V/III ratios, and is less hazardous than phosphine. Although source purities have improved considerably, consistent quality remains a concern. In the present work, metallic and organic impurities in the sources were measured at ppb levels, using analytical techniques such as FT–NMR, GC–MS, and ICP–OES. Impurity profiles were compared with the electrical properties of InP grown by using TMI and TBP at 600 °C and V/III ratio of 20. The films show 77 and 300 K Hall mobilities of 140,000 and 4850 cm 2/Vs respectively, and a background carrier concentration of 1.5×10 14 cm −3. For comparative evaluation, InP films were grown using TMI and PH 3 under optimized conditions at 580–600 °C and V/III ratio of 450–800 to achieve 77 and 300 K Hall mobilities as high as 287,000 and 5400 cm 2/Vs, and a background carrier concentration about 6–8×10 13 cm −3. The impact of deleterious impurities on electronic properties is discussed along with the “oxygen-free” synthetic strategies to metalorganic sources such as TMI, TBP and TBAs. Also reported are the results achieved with a novel delivery system (Uni-Flo™ cylinder) that has greatly improved the evaporation of solid sources such as TMI, Cp 2Mg and CBr 4 providing stable vapor concentration and greater than 95% utilization of precursors during MOVPE growth.

MOVPE growth of (AlGaIn)P/(GaIn)P heterostructures using TBP

(AlInGa)P red laser diodes have become increasingly attractive as light sources for various applications. High-quality AlInGaP and InGaP layers are of key importance for the performance of these lasers. In this report we explore the metalorganic vapor phase epitaxy (MOVPE) growth of red lasers using liquid precursors, i.e. replacing the highly toxic gaseous hydrides with liquid MO-V sources. This report will show material data (X-ray, PL, SIMS, etc.) on In(Al)GaP layers grown using TBP. The material performance of AlInGaP and InGaP layers grown using TBP and having different compositions will be compared to similar layers grown using PH 3. Growth parameters (temperature, V/III ratio) that will be presented will outline the advantages of MO-V growth such as lower growth temperatures and lower V/III ratios, as well as potential benefits on the maintenance of the reactor. Finally, we will show preliminary data on the full red laser epitaxial stack using the optimized growth conditions for each layer.

Environment, health and safety issues for sources used in MOVPE growth of compound semiconductors

As metalorganic vapor-phase epitaxy (MOVPE) is becoming well-established production technology, there are equally growing concerns associated with its bearing on personnel and community safety, environmental impact and maximum quantities of hazardous materials permissible in the device fabrication operations. Safety as well as responsible environmental care has always been of paramount importance in the MOVPE-based crystal growth of compound semiconductors. In this paper, we present the findings from workplace exposure monitoring studies on conventional MOVPE sources such as trimethylgallium, triethylgallium, trimethylantimony and diethylzinc. Also reviewed are the environmental, health and safety hazard aspects for metalorganic sources of routine elements, and the means to minimize the risks (i.e., engineering controls) involved while using these MOVPE sources.

Computational fluid dynamics on gaseous and surface chemistry of GaN‐MOVPE system for various pressures

Pressure effects on gaseous and surface chemistry of GaN grown by metalorganic vapor phase epitaxy (MOVPE) were studied. In order to obtain a chemical state of molecular species in an MOVPE reactor, computational fluid dynamics simulation was performed for 10 to 300 kPa, in which parasitic reactions among trimethylgallium and ammonia were considered. It was found that adducts of the dimethylgallium-NH2 family related to Ga–N molecule formation dominated reaction pathways. It was also revealed that a V/III ratio of physisorbed species was increased 2 orders of magnitude and close to a unity with the reactor pressure. These results suggested that MOVPE growth under atmospheric or higher pressures resulted in favourable growth conditions for high quality GaN. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Progress in nitride semiconductors from GaN to InN—MOVPE growth and characteristics

This paper reviews the field of nitride semiconductors ranging from GaN to InN with respect to metalorganic vapor phase epitaxy growth and characteristics starting from the period of single-crystalline films. Progress has been made on many fronts. For InGaN, a key material for the emitting layer of blue light-emitting-diodes, using nitrogen as the carrier and bubbling gases for metalorganic sources has been found to enhance indium incorporation, and composition control of InGaN has been achieved. The phase separation of the InGaAlN system has been semiempirically predicted using the strictly regular solution model. Regarding InN, which is a mysterious material, its band-gap energy has been found to be half the reported value. The polarity of the substrate has been found to affect the characteristics of epitaxially grown GaN. Finally, from a future perspective, InGaAlN laser diodes promise a laser diode with uncooled and high power operation, which is strongly required for optical communications systems.

Interlayer formation due to group V-hydride stabilization during interruptions of MOVPE growth of InGaP

The effect of indium and arsenic carry-over and of arsenic–phosphorus exchange on unintentional interlayer formation due to prolonged stabilization under arsine or phosphine during InGaP growth interruptions in metalorganic vapour phase epitaxy (MOVPE) at 580 °C is investigated. Photoluminescence, x-ray diffraction, secondary ion mass spectrometry, transmission electron microscopy and capacitance–voltage (C–V) depth profiling of the electron concentration are used to detect and to characterize possible unintentionally formed interlayers. The C–V measurements show that purging with PH3 mainly enhances the degree of ordering of an interlayer region due to a P-rich reconstruction of the InGaP surface during the growth interruption. The interlayer stress and band offset are too small to be detected by x-ray diffraction or photoluminescence. In contrast, purging with AsH3 during InGaP growth interruption leads to strong arsenic incorporation, but does not lead to any change in the In concentration. The As-rich interlayer gives rise to additional photoluminescence peaks and compressive strain. The relatively large interlayer thickness detected by C–V and SIMS measurements of up to 20 nm indicates that arsenic accumulated during the prolonged growth interruptions carries over into the InGaP layer grown after the interruption. It is shown that the chosen growth conditions suppress the In carry-over, but As carry-over occurs additionally to the As–P exchange.

In-situ spectroscopic ellipsometry investigation and control of GaN growth mode in metal-organic vapor phase epitaxy at low pressures of 20 Torr

In-situ spectroscopic ellipsometry (SE) was applied to metal-organic vapor phase epitaxial (MOVPE) growth of GaN. The effects of MOVPE reactor pressures on the growth modes of GaN were investigated by SE with the assistance of ex-situ scanning electron microscopy (SEM). We further demonstrated the on-line control of the GaN growth mode in MOVPE, which established a feasibility to grow high-quality GaN layers on sapphire substrate at the reactor pressure as low as 20 Torr.

MOVPE grown quantum cascade lasers

We report the metal-organic vapour phase epitaxy growth of quantum cascade lasers (QCLs) in both the GaAs–AlGaAs and InGaAs–AlInAs–InP materials systems. The GaAs based sample shows an increased emission wavelength relative to an equivalent design grown by molecular beam epitaxy, which we attribute to interfacial grading in the metal-organic vapour phase epitaxy device. The InP-based QCL (λ≈8.5 μm) operates in pulsed mode at room temperature, with low temperature threshold current density ∼1500 A/ cm 2 . This performance is comparable with that previously reported for similar structures grown by molecular beam epitaxy. The high quality interfaces necessary for successful QCL operation are achieved by using individually purged vent/run valves in the gas-handling section of the reactor, as well as a low growth rate for the active region of the structure.

MOVPE growth of Ga 3D structures for fabrication of GaN materials

This paper presents the growth and characterization of metallic gallium three-dimensional (3D) structures and preliminary results of their transformation into GaN-like structures. The structures were grown by metal-organic vapour phase epitaxy (MOVPE), using trimethyl gallium as gallium precursor on silicon (1 0 0). The growth temperature was between 550°C and 750°C. Interesting and new metallic structures were obtained with our growth parameters: balloon (montgolfier-like structure) and cauliflower-like. These metallic structures can grow up perpendicular to the substrate surface and have diameters between 0.1 and 5 μm, depending on the growth conditions. Moreover, selective metallic growth was obtained with our growth conditions. Some discussions about the growth mechanism are also presented. The Ga 3D nitridation process was carried out by annealing under NH 3 between 650°C and 750°C, far below the conventional nitridation temperature in MOVPE. Preliminary X-ray diffraction results show that a GaN-like structure can be obtained at such low nitridation temperature.