Low-pressure Metalorganic Vapor Phase Research Articles

High-speed growth of thick high-purity β-Ga2O3 layers by low-pressure hot-wall metalorganic vapor phase epitaxy

High-speed growth of thick, high-purity β-Ga2O3 homoepitaxial layers on (010) β-Ga2O3 substrates by low-pressure hot-wall metalorganic vapor phase epitaxy was investigated using trimethylgallium (TMGa) as the Ga precursor. When the reactor pressure was 2.4–3.4 kPa, the growth temperature was 1000 °C, and a high input VI/III (O/Ga) ratio was used, the growth rate of β-Ga2O3 could be increased linearly by increasing the TMGa supply rate. A thick layer was grown at a growth rate of 16.2 μm h−1 without twinning. Incorporated impurities were not detected, irrespective of the growth rate, demonstrating the promising nature of β-Ga2O3 growth using TMGa.

Low-Pressure MOVPE: The time of the pioneers

This paper is the author’s personal view on the development of low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) which took place in the late 70s and early 80s of last century. Pioneering work has been performed by the author and his co-workers in the labs of Thomson CSF, France, leading to many sophisticated devices including GaAs-GaAlAs- and InP-InGaAsP-based quantum well laser diodes which could be driven in CW mode, being grown successfully the first time by LP-MOVPE. This was only possible by a thorough analysis and a deep understanding of the underlying processes, in particular to overcome basic hurdles like the comparably low purity of the available MOVPE precursors at that time. Many results have kept their importance over decades and are still of major significance.

Raman spectra of semi-polar (11-22) InGaN thick films

We report the semi-polar (11-22) InGaN thick films (∼1 μm) grown on m-plane sapphire by a low pressure metal-organic vapor phase epitaxy (MOVPE) system. The Raman spectra of semi-polar InGaN thick films have been studied. For Raman spectra excited by the laser with wavelength of 532 nm, the E2(h) modes of GaN around 569 cm−1 and longitudinal optical (LO) phonon-plasma coupled modes (LPP) were mainly discussed. The E2(h) mode of GaN in the InGaN thick film would correspond to the lower frequency with wavenumber of 569.1 cm−1, compared to that in the InGaN thinner film (569.6 cm-1) in our case. Meanwhile, LPP modes also exhibited red shift with the increase of InGaN film thickness, which would be attributed to the stress relaxation and the decrease of free carrier concentration. The E2(h) modes of InGaN around 560 to 565 cm-1 and A1(LO) modes of InGaN around 729 to 731 cm-1 were found in Raman spectra excited by the laser with wavelength of 325 nm, but not probed in Raman spectra excited by a 532 nm laser. With the increase of In component, both modes were shifted towards low frequency. In addition, it was found that the Frölich electron-phonon interaction would significantly affect the peak position (729.2 cm-1) and full width at half maximum (FWHM, 17.2 cm-1) of A1(LO) mode of InGaN in the thicker film. Moreover, we have compared the Raman spectra of polar and semi-polar InGaN thick films so that the difference of Raman spectra between the two counterparts could be indicated due to lattice mismatch, In component incorporation efficiency, crystal quality and phase separation. The stress distribution of semi-polar InGaN materials is not as uniform as that of polar materials.

Room‐temperature laser operation of a (Ga,In)As/Ga(As,Bi)/(Ga,In)As W‐type laser diode

The ongoing pursuit for laser device emitting in the near-infrared spectral region on GaAs substrates has led to various material systems and device concepts. Alloys containing dilute amounts of Bismuth are promising candidates due to the already substantial band gap shift when incorporating low molar fractions of Bi in the GaAs host lattice. However, devices emitting at technologically essential wavelengths of 1.3 and 1.55 μm have yet to be demonstrated using this material system. Especially the non-equilibrium nature of the growth conditions required to grow the metastable material makes epitaxial growth with high molar fractions of Bi challenging. An alternate approach to reach the desired wavelengths exploits a type-II band alignment between two materials to push the emission wavelength further into the telecom bands. Here, room-temperature laser operation of the first type-II structure employing Ga(As,Bi) as hole confining layer and (Ga,In)As as electron confining layer is demonstrated. Sample growth is conducted by low-pressure metalorganic vapour phase epitaxy. Broad area laser devices are processed and characterized by electroluminescence measurements. A threshold current density of 3.86 kA/cm2 and emission wavelength of 1037 nm are observed, showing this device concept's potential for future lasers in the telecom bands.

Effects of dissipative electron tunneling manifested in the photocurrent of a GaAs p-i-n photodiode with a double InAs quantum dot layer

We report on the results of experimental studies of the photocurrent (PC) of photodiodes based on GaAs p-i-n structures with InAs/GaAs(001) double asymmetric quantum dot (DAQD) arrays obtained by self-assembling in the process of low-pressure metal-organic vapor phase epitaxy (LP-MOVPE). Three peaks were observed in the dependence of the PC on the reverse bias, measured under photoexcitation with a photon energy equal to the energy of the interband ground state transition in larger InAs QDs. These peaks were attributed to photoexcitation of electrons from the ground hole states in larger QDs into the ground electron states followed by resonant dissipative (with absorption or emission of optical phonons) and conservative tunneling into the GaAs conduction band via the ground electron states in smaller QDs. The PC dependence on the bias voltage agrees qualitatively with the theoretical field dependence of the probability of 1D dissipative tunneling between the QDs.

Van Der Waals Growth of III-V Semiconductors on Graphene

Recent discovery of graphene and its unique properties has attracted a great deal of interest in implementing this material in a variety of new devices, targeting applications in ultra-fast electronics, quantum information, carbon-free energy conversion, optoelectronics, and bio-integrated technologies [1,2]. However, graphene lacks a controlled non-zero bandgap, which prevents its large-scale application in electronic and energy conversion devices. To overcome this limitation, we exploit direct integration of III-V semiconductors on graphene through van der Waals epitaxy. Known for their efficient light emission and high charge carrier mobilities, III-V semiconductors are at the core of numerous technologies including high-efficiency solar cells, lasers, light emitting diodes, and ultra-fast transistors, to name a few [3].Due to lack of dangling bonds on graphene’s surface, in epitaxial growth of III-V semiconductors on graphene the crystals follow the order of graphene lattice through van der Waals forces. Initially, two nucleation and growth processes were suggested for such van der Waals epitaxy: (1) nucleation starts at defect sites on graphene [4], and (2) nucleation starts on specific sites on graphene lattice, which are the favorable adsorption sites for III/V adatoms [5]. The latter growth mechanism limits the epitaxial growth of the III-V crystals in four different relative orientations (with different strain values) [5]. Recently, density functional theory calculations followed by homoepitaxial growth of InP, GaP, and GaAs through several layers of graphene suggested another determining factor in van der Waals epitaxial growth: long-range interaction between the III-V substrate under graphene and the III-V structures grown on graphene [6].In this talk, we demonstrate the low-pressure metal-organic vapor phase deposition (MOCVD) of InAs, GaAs, InP, and GaP islands on single layer graphene sheets grown on copper foils and transferred on SiO2/Si (100), as well as graphene sheets directly grown on Ge (100), (110), and (111) substrates. We show that regardless of the nature of the substrate under graphene, III-V crystals grow mostly on graphene defect sites and their morphology can be somewhat controlled through controlling the growth parameters. We then show the effect of long-range forces between Ge and III-V structures on growth morphology, which results in significant coalescence and growth of tens of micron large islands on graphene/Ge as opposed to parasitic crystals grown on graphene/SiO2. In what follows, we provide a brief summary of our observations in both systems.All III-V semiconductors grown on graphene/SiO2/Si showed very similar growth morphology and crystal structure. Plan-view and cross-sectional scanning electron microscopy (SEM), micro-Raman spectroscopy, powder and high-resolution X-ray diffraction (XRD), along with cross-sectional transmission electron microscopy (TEM) and nanoscale cathodoluminescence analysis revealed formation of 1D, 2D, and 3D structures in zinc-blende, wurtzite, and polytypic (mixed zinc-blende/wurtzite) phases. We have recently demonstrated that polytypic InP crystals form a type II homojunction with potential applications in optoelectronic devices [7]. XRD analysis of the growth time evolution of texture, as well as growth rate and crystal size evolution analysis of the crystals using atomic force microscopy (AFM) suggested a growth mechanism similar to selected area MOCVD growth [7], which is widely used to grow nanostructures and devices. This enabled us to have some degree of control over the growth morphology (single crystals, polycrystals, nanowires) through controlling the growth parameters such as growth temperature, rate and time.Similar 1D, 2D, and 3D structure were grown on graphene/Ge (100), (110), (111). However, the size and crystalline quality of the islands have significantly improved for growth on Ge substrates. Moreover, two-step growth (nucleation at low temperature (450 °C) and growth at higher temperature (600 °C)) lead to coalescence of the crystals and formation of tens of microns large islands with smooth surface (roughness ~ 1nm from AFM data) on graphene/Ge, while no significant improvement in growth morphology was observed for growth on graphene/SiO2. These observations suggest a strong sensitivity of the morphology of the deposited films on the nature of the substrate below the graphene monolayers. This provides insight to control the properties of such hybrid systems and will pave the path to engineering a new class of electronic and optoelectronic devices by combining the advantages of semiconductors and graphene.

Исследование однородности состава по толщине слоев GaInAsP, полученных на подложках InP методом газофазной эпитаксии

GaInPAs/InP heterostructures grown by low pressure (0.1 bar, 600 oC) metal-organic chemical vapor phase deposition were investigated. The thicknesses of grown GaInAsP layers were about 1 µm. For the epitaxial layers Ga<sub>1-x</sub>In<sub>x</sub>P<sub>1-y</sub>As<sub>y)</sub> with average compositions of x = 0.77 – 0.87 and y = 0.07 – 0.42 the variation of V group elements content y with the epilayer depth were revealed, weher the compositions of V-group elements were changed up to Δy = 0.1 atomic fractions in V group elements sublattice. In most cases, y change occurs in a GaInAsP region up to 200 nm thick adjacent to the InP. In some cases, y changes throughout the whole GaInPAs layer thickness. Fo the epitaxial layers with a satisfactory crystal perfection the less was the mismatch between the substrate and the GaInPAs epitaxial layer, the smaller was the value of Δy. For GaInPAs layers characterized by a low degree of crystal perfection and a high lattice mismatch between GaInAsP and InP layers, the value of Δy was about zero. These data let us suggest that the incorporation of atoms of the V group in the epitaxial layer strongly depends on elastic deformation of the growing monolayer, that is mismatched with the underlying crystal surface.

Fabrication of star-shaped InP/GaInAs core-multishell nanowires by self-catalytic VLS mode

We successfully fabricated core-multishell nanowires using low-pressure metal organic vapor phase epitaxy (MOVPE) in self-catalytic vapor-liquid-solid (VLS) mode. The central core consists of an InP nanowire, and the shells are composed of alternating InP and GaInAs layers. The dependence of the shape and optical characteristics of the nanowires on the number of InP/GaInAs periods were investigated. By increasing the shell-periods, we observed a star-shaped cross section. The optical characteristics of the nanowires were investigated by room-temperature photoluminescence (PL) spectroscopy. The number of PL peaks was found to increase with increasing number of periods, and the peaks became redshifted.

Growth of ZnMgSeTe nearly lattice-matched to ZnTe and p-type doping by low-pressure MOVPE

Zn1-xMgxSeyTe1-y layers have been grown on (100) ZnTe substrates by low-pressure metalorganic vapor phase epitaxy using dimethylzinc, bis-methylcyclopentadienyl magnesium ((MeCp)2Mg), diethylselenide and diethyltelluride as source materials. The Mg mole fraction of Zn1-xMgxSeyTe1-y layer can be controlled successfully by varying (MeCp)2Mg transport rate. P-type doping of this material has been tried using tris-dimethylaminophosphorus as a dopant source. The influence of annealing temperature or dopant transport rate upon the electrical property has been investigated. All the layers show p-type conduction even without annealing. Through this study, a maximum carrier concentration of 2.5×1018cm−3 is obtained.

Photoluminescence and electrical properties of P-doped ZnTe layers grown by low pressure MOVPE

Photoluminescence (PL) spectra and electrical properties of both as-grown and annealed phosphorus-doped ZnTe layers grown by low-pressure metalorganic vapor phase epitaxy have been clarified as a function of reactor pressure or dopant transport rate. The carrier concentration of as-grown layer increases with decreasing reactor pressure or increasing dopant transport rate, in good agreement with PL behavior. Similar tendency is also found for annealed layer. Annealing treatment induces the enhancement of the carrier concentration, independent of reactor pressure or dopant transport rate. Through this study, a high carrier concentration near 1019cm−3 has been attainable.

Structural and optical properties of vanadium ion-implanted GaN

The field of advanced electronic and optical devices searches for a new generation of transistors and lasers. The practical development of these novel devices depends on the availability of materials with the appropriate magnetic and optical properties, which is strongly connected to the internal morphology and the structural properties of the prepared doped structures. In this contribution, we present the characterisation of V ion-doped GaN epitaxial layers. GaN layers, oriented along the (0001) crystallographic direction, grown by low-pressure metal-organic vapour-phase epitaxy (MOVPE) on c-plane sapphire substrates were implanted with 400keV V+ ions at fluences of 5×1015 and 5×1016cm−2. Elemental depth profiling was accomplished by Rutherford Backscattering Spectrometry (RBS) and Secondary Ion Mass Spectrometry (SIMS) to obtain precise information about the dopant distribution. Structural investigations are needed to understand the influence of defect distribution on the crystal-matrix recovery and the desired structural and optical properties. The structural properties of the ion-implanted layers were characterised by RBS-channelling and Raman spectroscopy to get a comprehensive insight into the structural modification of implanted GaN and to study the influence of subsequent annealing on the crystalline matrix reconstruction. Photoluminescence measurement was carried out to check the optical properties of the prepared structures.

Effects of the substrate misorientation on the structural and optoelectronic characteristics of tensile GaInP quantum well laser diode wafer

Three tensile GaInP quantum well laser diode wafers were grown in the same run by low-pressure metalorganic vapor phase epitaxy on GaAs substrates misoriented by 10°, 15°, and 22° toward (1 1 1)A respectively. The photoluminescence peak wavelength and intensity of the active region, the strain mismatch and the doping carrier concentration of the epitaxial layers, the whole thickness and the surface morphology of the wafers were all found to be strongly dependent on the misorientation of the substrates. Considering the comprehensive effects of material, electrical, and optical properties, the 15° substrate was superior to the 10° substrate for the growth of shorter wavelength red-light laser diode wafer, while substrate with too large misorientation of 22° was not a good choice for the epitaxy of red-light laser diode wafer.

Emission wavelength control of self-catalytic InP/GaInAs/InP core–multishell nanowire on InP substrate grown by metal organic vapor phase epitaxy

InP nanowires and InP/GaInAs/InP core–multishell nanowires were successfully grown on an InP(111)B substrate by low-pressure metal organic vapor phase epitaxy (MOVPE) using an indium catalyst. The self-catalytic vapor–liquid–solid (VLS) mode was used to obtain high-quality nanowires in which a deposited indium droplet acts as the catalyst instead of a metal particle, as in the case of the conventional VLS mode. InP core nanowire structures dependent on growth temperature and preheating temperature were obtained. InP/GaInAs/InP core–multishell nanowire structures, densities, and optical properties were investigated at various flow rates of trimethylindium (TMI) during the growth of InP core nanowires and the growth time of the GaInAs shell layer was also studied. The growth volume and density of nanowires were mainly dependent on growth temperature and preheating temperature, respectively. The height of nanowires was dependent on the TMI flow rate in the InP core nanowire growth, and the thickness of GaInAs shell layer was controlled by adjusting the growth time of the GaInAs shell layer. The photoluminescence (PL) intensity increased with increasing nanowire height and the peak wavelength was controlled by adjusting the thickness of the GaInAs shell layer.

Technology and properties of low-pressure metalorganic vapour phase epitaxy grown InGaAs/AlInAs superlattice for quantum cascade laser applications

Technology and properties of low-pressure metalorganic vapour phase epitaxy grown InGaAs/AlInAs superlattice for quantum cascade laser applications

Material research on the InGaAs-emitting-layer VECSEL grown on GaAs substrate

Wafers of InGaAs-emitting-layer vertical external cavity surface emitting semiconductor laser (VECSEL) gain chip and separate active region were grown on semi-insulator GaAs substrates by low pressure metal–organic vapor phase epitaxy (MOVPE). Photoluminescence (PL) wavelength of the active region could be adjusted linearly about 1nm for increasing 1sccm H2 flow rate through TMIn under AsH3 flow rates of 150sccm. The complicated surface-emitted PL signal of the VECSEL gain chip was strongly modulated by interferences within the multilayer and was interpreted by the aberrance of the quantum wells emission with a profile filtered by a micro-cavity resonance in the longitudinal confinement factor. Material tests of the VECSEL wafer showed the reflectivity of the DBR mirrors was in good agreement with the active region photoluminescence, and the wafer was obtained with high crystal quality.

The structural and optical properties of metal ion-implanted GaN

The practical development of novel optoelectronic materials with appropriate optical properties is strongly connected to the structural properties of the prepared doped structures. We present GaN layers oriented along the (0001) crystallographic direction that have been grown by low-pressure metal–organic vapour-phase epitaxy (MOVPE) on sapphire substrates implanted with 200keV Co+, Fe+ and Ni+ ions. The structural properties of the ion-implanted layers have been characterised by RBS-channelling and Raman spectroscopy to obtain a comprehensive insight into the structural modification of implanted GaN layers and to study the subsequent influence of annealing on crystalline-matrix recovery. Photoluminescence was measured to control the desired optical properties. The post-implantation annealing induced the structural recovery of the modified GaN layer depending on the introduced disorder level, e.g. depending on the ion implantation fluence, which was followed by structural characterisation and by the study of the surface morphology by AFM.

Growth of aluminium nitride with linear change of ammonia flow

The influence of AlN growth with a linear change of ammonia flux on the quality of AlN epilayers grown by low pressure metalorganic vapor phase epitaxy was studied. It was shown that by using this method it was possible to complete the coalescence of the grown AlN epilayer and eliminate pits from the surface as well as to prevent growth of nanocolumns. It was shown that decreasing ammonia flux has the most significant influence on the course of the coalescence process of the layer. The epilayers were analyzed using atomic force microscopy (AFM) to investigate their morphological properties and by high resolution X-ray diffraction (HRXRD) to study their structural properties. The etch pit density was examined by defect-selective etching.

Low-frequency noise in reverse-biased Schottky barriers on InAlN/AlN/GaN heterostructures

We present low-frequency gate noise characteristics of InAlN/AlN/GaN heterostructures grown by low-pressure metal-organic vapor phase epitaxy. The electric field in the InAlN barrier is determined from C-V measurements and is used for gate leakage current modeling. The latter is dominated by Poole-Frenkel emission at low reverse bias and Fowler-Nordheim tunneling at high electric field. Several useful physical parameters are extracted from a gate leakage model including polarizations-induced field. The gate noise fluctuations are dominated by trapping-detrapping processes including discrete traps and two continuums of traps with distributed time constants. Burst noise with several levels and time constant values is also observed in these structures. Low-frequency noise measurements confirm the presence of field-assisted emission from trap states. The 1/f noise model of McWorther is used to explain the 1/f-like noise behavior in a restricted frequency range.

Optimisation of a carbon doped buffer layer for AlGaN/GaN HEMT devices

This work reports on the optimisation of carbon doping GaN buffer layer (BL) for AlGaN/GaN HEMT (high electron mobility transistor) structures, grown by low pressure metal–organic vapour phase epitaxy (LP-MOVPE) on 3in. SiC semi-insulating substrates. The incorporation of carbon impurities in GaN is studied as a function of the growth conditions, without using an external carbon source. We observed that the C incorporation can be effectively controlled over more than one order of magnitude by tuning the reactor pressure and the growth temperature, without degradation of the crystalline properties of the GaN layers.HEMT structures with a specific barrier design were grown with different carbon dopings in the GaN BL and processed into transistors to evaluate the impact of the BL doping on the device performances. A significant improvement of the HEMT drain leakage current and of the breakdown voltage was obtained by increasing the carbon incorporation in the GaN BL. The RF performances of the devices show a trade-off between leakage currents and trapping phenomena which are enhanced by the use of carbon doping, limiting the delivered output power. An output power as high as 6.5W/mm with a Power Added Efficiency of 70% has been achieved at 2GHz by the HEMT structures with the lowest carbon doping in the BL.

GaN:Co epitaxial layers grown by MOVPE

We present a growth of GaN layers doped by cobalt using low pressure metalorganic vapor phase epitaxy on c-plane sapphire substrates. The in situ doping of GaN by Co was performed by the decomposition of bis(cyclopentadienyl)cobalt precursor. Three parameters, the temperature and pressure of the deposition and the Ga/Co ratio in the gas phase, influencing cobalt concentration were investigated. The obtained results were confronted with the thermodynamic predictions of Co solubility within GaN lattice and electronic structure calculations of GaN:Co. The magnetic properties of GaN:Co thin films were investigated using superconducting quantum interference device magnetometer. In addition, the layers were characterized by Raman and photoluminescence spectroscopy and atomic force microscopy. The concentration of Co was measured using electron microprobe and depth profile was measured using secondary ion mass spectroscopy. Room temperature ferromagnetic ordering was observed on the Co doped GaN layers.