Investigation of preparation and properties of epitaxial growth GaN film on Si(1 1 1) substrate

In this paper, a single crystalline GaN grown on Si(1 1 1) is reported using a GaN buffer layer by a simple vacuum reactive evaporation method. Scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence measurement (PL), and Hall measurement results indicate that the single crystalline wurtzite GaN was successfully grown on the Si(1 1 1) substrate. The surface of the GaN films is flat and crack-free. A pronounced GaN(0 0 0 2) peak appears in the XRD pattern. The full-width at half-maximum (FWHM) of the double-crystal X-ray rocking curve (DCXRC) for (0 0 0 2) diffraction from the GaN epilayer is 30 arcmin. The PL spectrum shows that the GaN epilayer emits light at the wavelength of 365 nm with an FWHM of 8 nm (74.6 meV). Unintentionally doped films were n-type with a carrier concentration of 1.76×10¹⁸/cm³ and an electron mobility of 142 cm³/V s. The growth technique described was simple but very powerful for growing single crystalline GaN films on Si substrate.     

Vapour phase growth of epitaxial silicon carbide layers

After a brief overview of different epitaxial layer growth techniques, the homoepitaxial chemical vapour deposition (CVD) of SiC with a focus on hot-wall CVD is reviewed. Step-controlled epitaxy and site competition epitaxy have been utilized to grow polytype stable layers more than 50 μm in thickness and of high purity and crystalline perfection for power devices. The influence of growth parameters including gas flow, C/Si ratio, growth temperature and pressure on growth rate and layer uniformity in thickness and doping are discussed. Background doping levels as low as 10¹⁴ cm⁻³ have been achieved as well as layers doped over a wide n-type (nitrogen) and p-type (aluminium) range.

Furthermore the status of numerical process simulation is mentioned and SiC substrate preparation is described. In order to get flat and damage free epi-ready surfaces, they are prepared by different methods and characterised by atomic force microscopy and by scanning electron microscope using channelling patterns. For the investigation of defects in SiC high purity CVD layers are grown. The improvement of the quality of bulk crystal substrates by micropipe healing and so-called dislocation stop layers can further decrease the defect density and thus increase the yield and performance of devices. Due to its high growth rate functionality and scope for the use of multi-wafer equipment hot-wall CVD has become a well-established method in SiC-technology and has therefore great industrial potential.     

Hydrodynamic description of epitaxial film growth in a horizontal reactor

Growth rate uniformity of epitaxial films is an important prerequisite for fabricating semiconductor devices. The correlation between the film thickness distributions and the vorticity distributions in the flow field is investigated in detail. Equations for conservation of mass, momentum and energy are solved numerically. The vorticity around the substrates and the vorticity gradient on the substrates are calculated from the velocity distribution rather than by solving the species equations. The substrate temperature is 1000 K, the total pressures are 2 and 20 Torr and the Reynolds numbers are 1, 10 and 100. The thicknesses of the films deposited by low-pressure chemical vapor deposition are measured. As a result, it can be shown that the deposited film thickness distributions agree with the vorticity gradient distributions. This suggests that vorticity has an important influence on film deposition.     

Ionized-cluster beam epitaxial growth of GaP films on GaP and Si substrates

Epitaxial films of GaP on GaP and Si substrates are grown by the Ionized-Cluster Beam Technology. The doping of Zn and N during the growth of the film are also discussed. A p-type epitaxial film doped by Zn and N shows an absorption spectrum similar to that of a direct transition type semiconductor. P-n junction LEDs are fabricated by depositing p-type GaP on n-type substrate. The luminescence from the device was observed.     

Study of Ge epitaxial growth on Si substrates by cluster beam deposition

Ge epitaxial layers with reasonable quality were grown on Si (1 1 1) substrates by cluster beam deposition (CBD) process. Molecular dynamics study of the low energy Ge clusters deposition process utilizing the Stillinger–Weber two- and three-body interaction potentials was carried out to compare the experimental results. Both experimental and simulation results prove that the substrate temperature plays a dominant role in the epitaxial growth of Ge films in CBD process. The influence mechanisms of temperature are discussed.     

Influence of oxygen contamination during Si low presure vapour phase epitaxy on epitaxial layer quality

The influence of oxygen contamination on Si low pressure vapour phase epitaxy (LPVPE) at 800°C in the SiCl₂H₂−H₂ system has been investigated. O₂ was added intentionally with partial pressures between 10⁻⁸ and 2×10⁻⁴ mbar. The quality of the epitaxially grown silicon layers was determined by comparing surface morphology, defect density, Schottky diode characteristics and SIMS measurements. These four parameters are correlated and they reveal a drastic decrease in epitaxial layer quality for O₂ pressures above 15×10⁻⁶ mbar. The critical oxygen pressure which has been until now considered as a limit for epitaxial growth can therefore be exceeded by one order of magnitude.     

Initial stage and kinetics of epitaxial film growth of A3B5 compounds

Thermodynamic and kinetic characteristics of GaAs film decomposition, mechanisms of film formation and growth, main features of the film growth under epitaxy in chemical transport were considered. The stages of epitaxial film growth and the relief smoothing of film surface were discussed applying data of electron microscopy investigations and theoretical considerations. The period of continuous film formation and degrees of the surface covering of the film growth by adsorbed substance were estimated.     

Hydride vapor phase epitaxial growth of thick GaN layers with in-situ optical monitoring

An in-situ optical monitoring system made in our laboratory is set up on the horizontal hydride vapor phase epitaxy (HVPE) equipment. From the growth rate information provided by this system, some basic growth parameters are optimized and high-quality GaN layers are grown. The growth stress of the HVPE GaN layer grown on different templates is also examined through the in-situ optical measuring.     

Liquid phase epitaxial growth of undoped gallium arsenide from bismuth and gallium melts

Electrical properties of undoped GaAs layers grown from Ga and Bi melts under identical conditions are compared as a function of growth temperature and pregrowth baking time. Identification of residual shallow donors and acceptors is performed by means of laser photoelectrical magnetic spectroscopy and low temperature photoluminescence. It is shown that a change of solvent metal results in complete alteration of major background impurities in grown epilayers due, mainly, to changes of distribution coefficients of these impurities. High purity, low compensation n-GaAs layers can be grown from Bi melt (epilayers with the Hall mobility of electrons μ77K ≈ 150000 cm²/V · sat n = 2.5 · 10¹⁴ cm⁻³ has been grown).     

Aluminum induced formation of SiGe alloy in Ge/Si/Al thin film structure

In this work, a study of aluminum induced crystallization (AIC) of thin film germanium/silicon/aluminum (Ge/Si/Al) structure on oxidized silicon is presented. The Ge/Si/Al trilayer structure was prepared in three consecutive thin film deposition processes. The AIC was performed in nitrogen at 500 °C within time duration between 1 and 9 h. The progress of crystallization was monitored by optical microscopy, Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS). It was found that in Ge/Si/Al structure the AIC can lead to formation of SiGe alloy at temperature of 500 °C. This presents an alternative low-temperature formation method of SiGe which is suitable for integration with the conventional Si technology in electronic device fabrication.     

Model for defect-free epitaxial lateral overgrowth of Si over SiO2 by liquid phase epitaxy

A growth model for defect-free epitaxial lateral overgrowth by liquid phase epitaxy is presented. Growth in the pure step flow mode and a preferential development of (111) planes in liquid phase epitaxy permit one to quantitatively predict the overgrowth. The shape and size of the Si lamellae which grow over SiO₂ depend on the crystallographic orientations of the substrate growth face and of the seeding windows. Overgrowth experiments with Si on oxidized, (111)- and (100)-oriented Si wafers serve to verify the model. Growth experiments from In and Bi solutions in temperature intervals between 950 and 800°C yield overgrowth widths up to 120 μm and aspect ratios of 40:1 on (111) oriented wafers.     

Agglomeration control during the selective epitaxial growth of Si raised sources and drains on ultra-thin silicon-on-insulator substrates

We have studied the impact of several Si selective epitaxial growth (SEG) process on the agglomeration of ultra-thin, patterned silicon-on-insulator (SOI) layers. Through a careful analysis of the effects of the in situ H₂ bake temperature (that followed an ex situ “HF-last” wet cleaning) and of the silicon growth temperature on the SOI film quality, we have been able to develop a low-temperature SEG process that allows the growth of Si on patterned SOI layers as thin as 3.4 nm without any agglomeration or Si moat recess at the Si window/shallow trench isolation edges. This process consists of an in situ H₂ bake at 650 °C for 2 min, followed by a ramping-up of the temperature to 750 °C, then some SEG of Si at 750 °C using a chlorinated chemistry (i.e. SiH₂Cl₂+HCl).     

Hydrogen and nitrogen ambient effects on epitaxial growth of GaN by hydride vapour phase epitaxy

This study presents the influence of the composition of the carrier gas on the growth of GaN by HVPE. Since no hydrogen is introduced in the vapour phase, the deposition is expected to be controlled by Cl desorption in the form of GaCl₃, as has been proposed for GaAs. However, our published model predicts much lower growth rates than those observed. We can account for both the observed parasitic deposition and GaN growth rate if we assume that GaCl₃ is not at its equilibrium pressure in the deposition zone and where nucleation takes place on the walls as well as on the substrate. This yields a high rate of parasitic nucleation even though the nominal supersaturation is vanishing small. Very little growth takes place on the substrate where the equilibrium pressure of GaCl₃ is reached. We describe similar experiments performed with a H₂/N₂ mixture as the carrier gas. In this case, we expect GaN deposition to be controlled by desorption of Cl as HCl, which is known as the H₂ mechanism. It is speculated that the results show the existence of a new growth mechanism.     

Optically monitoring and controlling epitaxial growth

We provide a perspective on current capabilities for optically monitoring and controlling epitaxial growth, and discuss examples taken from recent work at Bellcore.     

Optimized growth conditions of GaN epitaxial layers

Optimized growth conditions of the epitaxial GaN layers on the (0001) oriented sapphire substrates in the Ga/HCl/NH₃/H₂ system have been proposed. The corresponding growth rate varied about the value 0.5 μm · min⁻¹. The study of surface morphology and X-ray diffraction have confirmed the single crystalline character of the layers even though the surface shows a faceted structure. The c/a ratio calculated from our measured data of the lattice parameters was found 1.624 which is relatively close to the ideal close-packed wurtzite structure value. The cathodoluminescent spectra of the layers with a sufficient thickness were characterized by a peak at 3.35 eV having a halfwidth of about 0.2 eV.