R. Korbutowicz

MOVPE GaN Grown on Alternative Substrates

The structure, morphology and optical properties of GaN films deposited by metalorganic vapour phase epitaxy (MOVPE) on alternative substrates: ZnO, NdGaO, YSZ (yttria stabilized zirconia). Scanning electron microscopy, X-ray diffraction and photoluminescence were used for the epitaxial layers characterisation. The obtained results have been compared to those of GaN layers grown on c-plane sapphire substrates. It was established that the most important step towards the realisation of device quality GaN material on alternative substrates is the first stage of the growth process.

Wet Thermal Oxidation of GaAs and GaN

The chapter is devoted to the thermal wet oxidation of AIIIBV semiconductor compounds, mainly to gallium arsenide and gallium nitride. It has been divided into several topics, containing of monoclinic gallium oxide1 -Ga2O3 properties data, techniques of oxide fabrication and application description. In the first part, properties of mentioned semiconductor’s oxides are characterized. Then methods of manufacturing with a special attention for wet thermal oxidation are described. After that, applications of gallium oxide structures in electronics are given. It focuses also on the semiconductor structures dedicated for gas sensors application while gallium oxide layers improve significantly the most critical parameters of the detector compared to those containing of e.g. SnO2. AIIIBV and AIIIN semiconductors compounds are wide known as materials for optoelectronics devices. They are used often also to the construction of high temperature and microwave devices or chemical gas sensors. In these applications dielectric layers are necessary. There is a possibility of using their own oxides – Ga2O3 gives a chance to manufacture many different devices – MOS structures (Metal-Oxide-Semiconductor). It can be MOS capacitors, power Metal Oxide Semiconductor Field Effect Transistors (MOSFETs), high mobility GaAs MOSFETs or gate turn-off thyristors and, probably, CMOS applications (Pearton et al., 1999; Wu et al., 2003). The MOS-gate version of the HEMT has significantly better thermal stability than a metal-gate structure and is well suited to gas sensing (Schweben et al., 1998; Baban et al., 2005; Hong et al., 2007).

Wet thermal oxidation for GaAs, GaN and Metal/GaN device applications

Thermal wet oxidation of gallium arsenide GaAs (wafers) and gallium nitride GaN (layers from metalorganic vapor phase epitaxy MOVPE and hydride vapor phase epitaxy HVPE) was carried out in N2 as a main gas and H2O as an oxidizing agent. Materials parameters and surface morphology were studied by means x-ray diffraction, ellipsometry, photoreflectance PR, micro Raman spectroscopy, optical microscopy and atomic force microscopy AFM. The lack of materials parameters or their wide range, especially refractive index, dielectric constant and their dependence of oxides composition and structure constituted some problems during measurements. GaAs oxidation was more difficult as GaN oxidation, especially GaN from HVPE.

Growth of high-quality GaN and AlxGa1-xN layers by an MOVPE technique

AlxGa1-xN layers with 0.02 xGa1-xN layer grown on it were evaluated by high resolution X-ray measurements, their surface morphology was observed with SEM and Nomarski optical microscope. Electrical properties of the layers were determined by C-V measurements performed at 100 kHz and 1 MHz using mercury probes. The aluminum incorporation into the solid phase during the growth process has been studied. As a result high quality AlxGa1-xN/GaN layers for electronic application have been deposited.

Ga-As-Bi phase equilibrium study by LPE for thin solutions

Abstract Mixed solvents such as Ga+Bi are used to improve GaAs epilayer surface morphology and the growth control. Liquid phase epitaxy was carried out for the mixed solutions of 1.4 mm thickness. Substrates and reagents were placed in a graphite cassette. The growth was performed in an open quartz tube reactor in a resistive furnace under hydrogen atmosphere. Growth kinetics was studied for GaAs epitaxy. The liquidus isotherms for the Ga-As-Bi system were determined for T = 1013 K and T = 1073 K in the Ga-As-GaAs region. The average liquidus slope was determined for the investigated region along the arsenic diffusion coefficient D L As as a function of temperature and Bi content in the solution. The surface morphology was improved for layers grown from the mixed solutions in comparison with those from gallium solutions. Precise control of the epilayer thicknesses was achieved.

Study of the nature of light hole excitonic transitions in InGaAs/GaAs quantum well

Abstract Photoreflectance (PR) spectra of strained In GaAs/GaAs MQWs were measured. Heavy and light hole excitonic transitions were observed. Applying results of theoretical calculations which include excitonic and strain effects, we obtained that the existence of type II light hole exciton in our type I MQW system should be considered.

Photoreflectance investigations of GaN epitaxial layers

Abstract The photoreflectance spectroscopy was used to investigate GaN epitaxial layers. Heterostructures being under study were grown by metalorganic vapour phase epitaxy (MOVPE) and hydride vapour phase epitaxy (HVPE) techniques on sapphire substrate. All measurements were performed at room temperature, what is an advantage in comparison to other spectroscopic techniques. The photoreflectance spectra exhibit resonances, which originate from the direct optical transition between the conduction band and valence band. From the energy position of these resonances, the direct band-gap energies of semiconductor being under study were obtained. Franz–Keldysh oscillations (FKO) above the band gap in doped (HVPE) structure are observed. From the period of Franz–Keldysh oscillations the strength of the surface electric field was determined.

The influence of MOCVD process scheme on the optical properties of GaN layers

The GaN layers were grown on sapphire substrates using atmospheric pressure MOCVD system. The new process scheme was developed to improve the quality of epitaxial layers. Additional buffer layers, grown with increasing temperature and increasing V/III ratio, were inserted between the low temperature buffer layer and the high temperature GaN overlayer grown on it. The influence of growth conditions on luminescence properties of GaN layers, especially the yellow emission, was investigated.

Critical layer thickness of InGaAs on GaAs examined by photoreflectance spectroscopy

Abstract Photoreflectance (PR) spectroscopy has been used to investigate MOCVD grown InGaAs on GaAs layers, with different indium content. The layer thicknesses of measured samples are above and below the critical value, and hence part of our layers is strained and part is unstrained. From PR spectra the value of interband transition energy of InGaAs, broadening parameter of the transition and amplitude of ΔR R signal have been determined. The dependence of broadening parameter and amplitude versus Δd (difference between nominal layer thickness Δd and its critical thickness d c ) has been presented. In the vicinity of Δd = 0( d c ) the plastic relaxation effects have appeared and the character of both dependences has changed dramatically.

Properties of GaN layers deposited on AlN/sapphire template substrates

Gallium nitride thick layers were deposited on template substrates which consisted of low temperature aluminium nitride (LT-AlN) buffer layer or AlN/Al0.2Ga0.8N double-layer buffer grown on (0001) oriented sapphire substrates. Buffers were deposited by using Metal Organic Vapor Phase Epitaxy (MOVPE) in various temperatures and thick GaN layers by Hydride Vapor Phase Epitaxy (HVPE) at 1050°C in two-step growth procedure. Morphology of samples was evaluated by AFM (Atomic Force Microscopy) and Scanning Electron Microscopy (SEM), crystalline quality by High-resolution X-Ray Diffractometry (HRXRD), optical quality by Photoluminescence (PL) spectra, and residual strain by micro-Raman scattering measurements.