Metalorganic Chemical Vapor Deposition Epitaxy Research Articles

Dislocations/Defects analysis in III-V nitrides - a cost effective MOCVD epitaxy solution

In present paper an innovative technique to reproduce the epitaxial growth results through lateral flow metal organic chemical vapor deposition (MOCVD) reactor process at atomistic scale is reported. It includes the equivalent MOCVD reactor geometry architecture of AIXTRON 200/4 RF-S horizontal flow reactor. The gas- and surface phase chemical reaction kinetics and thermodynamics are given due consideration in the present study without use of any continuum or fluid dynamics models. The optimum conditions are extracted by running design of experiments over TNL-EpiGrow simulator to achieve high crystalline quality aluminum nitride (AlN) films over Si (111) substrate. The impact of variation in precursor NH3 flow rates and carrier gas N2 pressure are used to predict the conditions to optimize the improved morphology and quality of the AlN films. The defects densities are characterized in terms of vacancies and dislocation densities. The roughness and lattice parameters are extracted. The growth rates obtained in present studies are compared against reported the similar experiments. The excellent agreement is observed between experimental and simulated results. The dislocation densities in grown samples are also found in good agreement with the similar experimental reported densities in each sample.

Homoepitaxial growth of (100) Si-doped β-Ga2O3 films via MOCVD

Homoepitaxial growth of Si-doped β-Ga2O3 films on semi-insulating (100) β-Ga2O3 substrates by metalorganic chemical vapor deposition (MOCVD) is studied in this work. By appropriately optimizing the growth conditions, an increasing diffusion length of Ga adatoms is realized, suppressing 3D island growth patterns prevalent in (100) β-Ga2O3 films and optimizing the surface morphology with [010] oriented stripe features. The slightly Si-doped β-Ga2O3 film shows smooth and flat surface morphology with a root-mean-square roughness of 1.3 nm. Rocking curves of the (400) diffraction peak also demonstrate the high crystal quality of the Si-doped films. According to the capacitance–voltage characteristics, the effective net doping concentrations of the films are 5.41 × 1015 – 1.74 × 1020 cm−3. Hall measurements demonstrate a high electron mobility value of 51 cm2/(V·s), corresponding to a carrier concentration of 7.19 × 1018 cm−3 and a high activation efficiency of up to 61.5%. Transmission line model (TLM) measurement shows excellent Ohmic contacts and a low specific contact resistance of 1.29 × 10-4 Ω·cm2 for the Si-doped film, which is comparable to the Si-implanted film with a concentration of 5.0 × 1019 cm−3, confirming the effective Si doing in the MOCVD epitaxy.

Metalorganic chemical vapor deposition of (100) β-Ga2O3 on on-axis Ga2O3 substrates

Metalorganic chemical vapor deposition (MOCVD) growths of β-Ga2O3 on on-axis (100) Ga2O3 substrates are comprehensively investigated. Key MOCVD growth parameters including growth temperature, pressure, group VI/III molar flow rate ratio, and carrier gas flow rate are mapped. The dependence of the growth conditions is correlated with surface morphology, growth rate, and electron transport properties of the MOCVD grown (100) β-Ga2O3 thin films. Lower shroud gas (argon) flow is found to enhance the surface smoothness with higher room temperature (RT) electron Hall mobility. The growth rate of the films decreases but with an increase of electron mobility as the VI/III molar flow rate ratio increases. Although no significant variation on the surface morphologies is observed at different growth temperatures, the general trend of electron Hall mobilities are found to increase with increasing growth temperature. The growth rates reduce significantly with uniform surface morphologies as the chamber pressure increases. By tuning the silane flow rate, the controllable carrier concentration of (100) β-Ga2O3 thin films between low-1017 cm−3 and low-1018 cm−3 was achieved. Under optimized growth condition, an (100) β-Ga2O3 thin film with RMS roughness value of 1.64 nm and a RT mobility of 24 cm2/Vs at a carrier concentration of 7.0 × 1017 cm−3 are demonstrated. The mobilities are primarily limited by the twin lamellae and stacking faults defects generated from the growth interface. Atomic resolution scanning transmission electron microscopy reveals the formation of twin boundary defects in the films, resulting in the degradation of crystalline quality. Results from this work provide fundamental understanding of the MOCVD epitaxy of (100) β-Ga2O3 on on-axis Ga2O3 substrates and the dependence of the material properties on growth conditions. The limitation of electron transport properties of the (100) β-Ga2O3 thin films below 25 cm2/Vs is attributed to the formation of incoherent boundaries (twin lamellae) and stacking faults grown along the on-axis (100) crystal orientation.

Light-assisted scanning probe microscopy characterization of the electrical properties of AlGaN/GaN/Si heterostructures

The article proposes a new methodology that combined light-assisted Scanning Surface Potential Microscopy (SSPM), Scanning Spreading Resistance Microscopy (SSRM) and Scanning Capacitance Microscopy (SCM) techniques for the extended nanoscale characterization of the electrical properties of AlGaN/GaN/Si heterostructures. Two measurement regimes were used to investigate the influence of surface defects on local electrical properties of samples: surface mapping with additional light excitation and one-point spectroscopy which enabled the accurate investigation of energetic transitions associated with a specific surface structure. The influence of two types of surface defects existing in the AlGaN/GaN/Si samples grown by metalorganic chemical vapour deposition epitaxy on the two-dimensional electron gas (2DEG) formation process on the AlGaN/GaN interface was explained. In the case of the sample with the SiN nanomasking layer added to the growth scheme, the areas of negative charge associated with defects created the localised, isolated islands that did not influence the process of electric field formation in the AlGaN/GaN system and had no significantly detrimental impact on the electron transport. The presence of surface defects in the sample without the SiN layer caused the disturbance of the 2DEG electrical properties not only in the place of the defect’s presence but also at some distance away from it. In that case, the photovoltage and photoconductivity spectra indicated the existence of a disordered structure of the AlGaN layer, near and away from the defects. Additionally, it was clarified that the characteristic electronic transition at 3.0 eV related to a deep trap state existing in the AlGaN barrier was localised solely at the surface site of the defects. It was observed during the SSRM measurements that both types of defects created a leakage current paths with prolonged conductivity (up to several seconds), which effect was not reported earlier, that provide an original insight into the origins of the long relaxation time effects existing in the AlGaN/GaN heterostructures.

Fully transparent GaN homojunction tunnel junction-enabled cascaded blue LEDs

A sidewall activation process was optimized for buried magnesium-doped p-GaN layers yielding a significant reduction in tunnel junction-enabled light emitting diode (LED) forward voltage. This buried activation enabled the realization of cascaded blue LEDs with fully transparent GaN homojunction tunnel junctions. The initial optimization of buried p-GaN activation was performed on PN junctions grown by metal organic chemical vapor deposition (MOCVD) buried under hybrid tunnel junctions grown by MOCVD and molecular beam epitaxy. Next the activation process was implemented in cascaded blue LEDs emitting at 450 nm, which were enabled by fully transparent GaN homojunction tunnel junctions. The tunnel junction-enabled multi-active region blue LEDs were grown monolithically by MOCVD. This work demonstrates a state-of-the-art tunnel junction-enabled cascaded LED utilizing homojunction tunnel junctions which do not contain any heterojunction interface.

Connection between GaN and InGaN growth mechanisms and surface morphology

Power spectral density (PSD) analysis of atomic force microscopy (AFM) images is used to determine the roughening and smoothing mechanisms that contribute to InGaN and GaN morphology during metalorganic chemical vapor deposition epitaxy (MOCVD). The analysis finds that non-stochastic surface roughening occurs from deposition onto the pre-existing GaN surface with this roughening becoming more evident at lower growth temperature. Counteracting the surface roughening are two smoothing mechanisms that operate over different temperature ranges and length scales. The first is an evaporation and recondensation mechanism, which dominates at higher temperatures (>900°C) and longer length-scales ranging from one to tens of microns. The second is a surface diffusion mechanism, which dominates at lower temperatures (<800°C) and shorter length scales ranging from tens to hundreds of nanometers. The competition between roughening and smoothing leads to a characteristic length-scale for mound (or hillock) formation, which prevails for low-temperature growth of GaN and InGaN single heterolayers, as well as InGaN/GaN multiple quantum wells (MQWs). For InGaN/GaN MQW samples where the wells are similarly grown, the choice of the GaN-barrier growth conditions is shown to influence MQW-interface roughness. Moreover, increased green-wavelength photoluminescence intensity is observed when rougher (rather than smoother) interfaces are present. The results suggest that the operation of smoothing mechanisms during MOCVD growth can be tailored to influence InGaN/GaN surface morphology and possibly improve emission efficiency.

Enhanced performance of an AlGaN/GaN high electron mobility transistor on Si by means of improved adatom diffusion length during MOCVD epitaxy

Four types of AlGaN/GaN high electron mobility transistor (HEMT) structures have been epitaxially grown on Si substrates by metalorganic chemical vapor deposition (MOCVD) and fabricated into devices. To achieve crack-free device structures, various stress-engineering methods have been employed including the use of AlGaN/AlGaN-graded layers, insertion of low-temperature AlN layers and ion implantation of the AlN/Si substrate. To improve material quality, pulsed MOCVD is used to enhance adatom diffusion length during (Al) GaN epitaxy of various layers in the HEMT structure. A comparison between structural and morphological characteristics of the HEMTs shows improvement in the (0 0 0 2) symmetric rocking curve value to 837.9 s−1 and the surface roughness of 0.21 nm for HEMT structures grown using pulsed epitaxy. An OFF-state breakdown voltage of 217 V at a drain current of 1 mA mm−1 at Vg = −8 V was measured for the structure with enhanced material quality.

Self-organized InGaN nanodots grown by metal-organic chemical vapor deposition system

It has been demonstrated that self-organized InGaN nanodots can be vertically grown by utilizing metal-organic chemical vapor deposition epitaxy (MOCVD). We report the investigation of the characteristics of InGaN with various indium contents and the fabrication of self-organized InGaN nanodots will also be discussed. Using a temperature ramping growth method, self-organized InGaN nanodots were formed vertically protruding above the sample. It was found that typical height of these nanodots is around 45 nm with an average width of 5 nm. It was also found that the local density of the vertically grown self-organized InGaN nanodots could reach 8.2 × 1012 cm−2. These self-organized InGaN nanodots will result in a red shift in PL spectrum indicating that In droplets act as an indium source to form an InGaN intermediate layer near the heterointerface.

Determination of lattice polarity for growth of GaN bulk single crystals and epitaxial layers

The polarity of the lattice of bulk single GaN crystals and the polarity of homoepitaxial and heteroepitaxial-on-sapphire GaN thin films has been studied using convergent beam electron diffraction. Diffraction patterns obtained at 200 kV for the 〈1–100〉 projection of GaN were matched with calculated patterns. The lattice orientations of two commonly observed bulk single-crystal facets were identified. It is shown that the smooth facets in single crystals correspond to the (0001), Ga-terminated, lattice planes, whereas the rough facets correspond to the (0001̄), N-terminated, planes. It is also shown that metalorganic chemical vapor deposition epitaxy retains the polarity of the substrate, i.e., no inversion boundaries were observed. Heteroepitaxy on sapphire is shown to grow in the (0001), Ga-terminated orientation.

Defects in Metalorganic Chemical Vapor Deposition Epitaxy-Grown ZnSe Films on GaAs Investigated by Monoenergetic Positrons

Defects in metalorganic chemical vapor deposition epitaxy (MOVPE)-grown ZnSe heteroepilayers on GaAs were investigated by monoenergetic positrons. The present work revealed clear differences between an as-grown specimen and a heat-treated one under different atmospheres. The as-grown specimen prepared at high temperature (350°C) showed a proliferation of a large number of defects near the surface and at the GaAs interface due to lattice mismatching and nonstoichiometry. Heat treatment at 70°C in N2 ambient introduced vacancies in high concentrations which contribute to the deep emission of photoluminescence. It is concluded that adequate heat treatment under zinc vapor is essential to reduce the concentration of native defects in MOVPE-grown ZnSe film on GaAs.

Quantum well lasers with active region grown by laser-assisted atomic layer epitaxy

Laser-assisted atomic layer epitaxy (LALE) is used to locally deposit device-quality material for the first time, as demonstrated by successfully fabricating broad-area lasers with a GaAs quantum well grown in this way. By hybridizing LALE with conventional metalorganic chemical vapor deposition epitaxy, heterostructures are grown which allow characterization of material quality by photoluminescence and capacitance-voltage measurements. In addition, graded-index separate-confinement heterostructure lasers with threshold current densities of 650 A/cm2 for 580-μm-long devices were made using the LALE quantum well deposit, while devices made away from the deposit did not lase.

Liquid and Vapor Phase Growth of III-V Materials for Photonic Devices

Precisely controlled epitaxial growth of microscopically thin semiconductor layers is essential for lightwave source and detector components. Achieving precise control while simultaneously meeting manufacturing volume and cost requirements is a demanding challenge. We are meeting that challenge with the development of advanced liquid and vapor phase epitaxial growth technologies. In this article we provide a review of the principles, a brief description of the state-of-the-art implementation, and a discussion of the advantages and limitations of the four epitaxial techniques we use — liquid phase epitaxy, trichloride and hydride vapor phase epitaxy, and metal-organic chemical vapor deposition epitaxy.

GaAs/GaAlAs selective MOCVD epitaxy and planar ion-implantation technique for complex integrated optoelectronic circuit applications

We report on a monolithic integration technique incorporating selective GaAs/GaAlAs optical device epitaxy (based on metalorganic chemical vapor deposition (MOCVD)) and planar ion-implanted GaAs devices, formulated for application to complex integrated optoelectronic circuits. This integration scheme offers fabrication compatibility of epitaxially grown optoelectronic devices with maturing GaAs electronic circuit approaches which require selective multiple implants and small gate geometries. Details of the monolithic integration technique and an example of its application to an optoelectronic transmitter are described.

5286. High-purity ZnSe obtained by metalorganic chemical vapour deposition epitaxy: P Blanconnier et al,J Appl Phys,52 (11), 1981, 6895–6900

5286. High-purity ZnSe obtained by metalorganic chemical vapour deposition epitaxy: P Blanconnier et al,J Appl Phys,52 (11), 1981, 6895–6900

High-purity ZnSe obtained by metalorganic chemical vapor deposition epitaxy

High-quality homoepitaxial layers of ZnSe have been obtained by the metalorganic method. Optical measurements demonstrate the good purity of these samples. Resonant electronic Raman-scattering experiments have allowed the identification of some residual donors and shown that most of them originate in the substrate. A shallow donor, with an ionization energy of about 30.4 meV, not yet mentioned in the literature, has been observed and is believed to be iodine. Excitation Spectroscopy and Selective Pair Luminescence techniques have shown the existence of a new shallow acceptor associated to a donor-acceptor pair transitions band peaking at 2.75 eV, the ionization energy of which would be about 56 meV. The resonant electronic Raman-scattering technique, used here for the first time to investigate donors, appears much more sensitive than classical luminescence to characterize the semiconductor materials.