Joanna Prazmowska

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.

Creation of high resolution pattern by nanoscratching

The lithography is a basic microelectronic process which determines properties of fabricated device. The resolution of optical lithography applied nowadays is insufficient for creating high resolution patterns such as gate electrode in transistors. The scaling ability is the major motivation for undertaking experiments to elaborate high resolution lithography techniques. The atomic force microscope (AFM) is commonly used as tool for creation patterns in sub-micrometers resolution. In this paper, the results of simulations of electromagnetic field behavior during passing the gap with a size smaller than the wavelength of the optical lithography light source are presented. Also results of the nanoscratching lithography prepared for various parameters of force that are applied to the tip are summarized.

Investigation of the influence of low-concentration hydrogen on the surface potential of thin metallic films for sensor applications

In this paper, a study of the influence of hydrogen (concentrations 6 ppm − 1%) on the work function of thin metallic films at moderately elevated temperatures is presented. The work function was measured indirectly by the observation of the surface potential of dedicated test structures using scanning surface potential microscope. Metallic layers with thicknesses of 10, 20, 30, and 50 nm were deposited on semiconductor substrates as well as on a thick gold layer. The investigations were focused on palladium thin films although a comparison to results obtained for platinum layers was also discussed.

Influence of hydrogen absorption on stress changes in thin catalytic metal films dedicated for sensors application

In the paper results of investigation of the influence of low concentration hydrogen on stress changes in thin catalytic metal films were discussed. The concentration of H2 was altered from 6 ppm to 1% of hydrogen (6N) in nitrogen (6N). Silicon beams covered with palladium or platinum films of various thicknesses were anchored at one end and their deflection at the other end was measured by atomic force microscope. Stress changes were determined by application of modified Stoney formula and compared with results of computer modelling. The influence of stress caused by hydrogen absorption on the alteration of output characteristics of AIII-N based hydrogen sensors was excluded. The time dependence of stress in metallic films for various hydrogen concentrations indicated dissociation limited mechanism of hydrogen absorption.

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.

Properties of GaN layers deposited on (0001) sapphire templates

High temperature gallium nitride (HT-GaN) layers were grown by HVPE (hydride vapor phase epitaxy) on low temperature GaN (LT-GaN) nucleation layers deposited by HVPE. The (0001) sapphire substrates were used. The LT-GaN process parameters were as follows: HCl flow rate was 10 sccm/min, temperature 450degC and deposition time intervals 7 and 9 minutes for sample #1 and #2, respectively. The values were chosen after previous optimization of this stage of technology. Before nucleation layer deposition sapphire substrates were pre-heated for 10 min in the N2:NH3 ambient. The nucleation layer epitaxy was followed by recrystallization and migration process for 10 minutes. Morphologies of LT- and HT-GaN layers were examined by scanning electron microscopy. Properties of HT-GaN layers were investigated by photoluminescence spectra and micro-Raman measurements.

Functionally Graded Structures of AIII-BV(N) Materials for Detectors

Functionally graded materials are widely applied for mechanical applications. Nowadays they become more and more attractive for electronic and optoelectronic devices fabrication. This is caused by their unique properties. FGM are potential candidates for high sensitive photonic devices which could operate in a wide spectral range (also for voltage tunable photodetectors). In this paper the analysis of several photodetectors constructions fabricated in FGM were presented. The influence of AIII-BV (N) grading layers composition and configuration of the detector on its optical and electrical properties was discussed. Also the comparison between conventional non-graded and graded devices was shown. All simulations presented in the work were performed by the specialized software designed for modeling of AIII-BV (N) graded structures. The software allows us to calculate both the parameters of FMG structure and device characteristics

Fabrication of Si3N4 Layers by Pulse Magnetron Sputtering Method

Amorphous silicon nitride thin layers are the most widely applied dielectric layers in modern semiconductor devices. It is caused by their excellent properties such as high chemical inertness, high thermal stability and corrosion resistance. Si3N4 also has remarkable mechanical, optical and dielectric properties. Silicon nitride thin layer can be fabricated by low-pressure chemical vapour deposition (LPCVD), plasma enhanced chemical vapour deposition (PECVD), reactive evaporation and ion beam deposition. More recently reactive sputtering techniques were proposed for Si3N4 fabrication. We have applied the pulsed reactive magnetron sputtering of a Si target in nitrogen atmosphere for preparation of Si3N 4 layers. Parameters of the deposition process were examined. Their influence on layer properties was studied and discussed

Study of interface of ohmic contacts to AlGaN/GaN heterostructure

The paper embraces studies of the interface of ohmic contacts and AIIIBV-N heterostructure. The TiAl based metallization stack was investigated. The Ti/Al/Ni/Au contact to AlGaN/GaN heterostructures fabricated by metal-organic vapour phase epitaxy was examined using three methods i.e. etching of annealed contact metallization, fractures (prepared at room temperature and after a bath in liquid nitrogen) and microsections imaging. The main focus was on the estimation of reaction range on the metal-semiconductor interface of samples. In the first method, the surface of AlGaN/GaN heterostructure after etching of metallization was studied by an optical microscope, scanning electron microscope and atomic force microscope. The changes of surface morphology of heterostructure directly reflect solid state reactions range between metallization and semiconductor. The range of reactions was also observed using the small-angle microsections method while the fractures analysis did not bring valuable information.