G. Ecke

Growth of cubic InN on r-plane sapphire

InN has been grown directly on r-plane sapphire substrates by plasma-enhanced molecular-beam epitaxy. X-ray diffraction investigations have shown that the InN layers consist of a predominant zinc blende (cubic) structure along with a fraction of the wurtzite (hexagonal) phase which content increases with proceeding growth. The lattice constant for zinc blende InN was found to be a=4.986 A. For this unusual growth of a metastable cubic phase on a noncubic substrate an epitaxial relationship was proposed where the metastable zinc blende phase grows directly on the r-plane sapphire while the wurtzite phase arises as the special case of twinning in the cubic structure.

Phase selective growth and properties of rhombohedral and cubic indium oxide

Phase selective growth of rhombohedral and cubic indium oxide polytypes was studied. The selective growth of different polytypes was achieved by adjusting substrate temperature and trimethylindium flow rate during metal organic chemical vapor deposition on c-plane sapphire. The optical band gaps of the cubic and rhombohedral phases were determined to be ∼3.7 and ∼3.0eV, respectively. On the basis of the performed structural investigations, a phenomenological model of the nucleation and growth of highly textured cubic In2O3 on Al2O3 (0001) is proposed.

Properties of rf-sputtered indium–tin-oxynitride thin films

Indium–tin-oxide (ITO) and indium–tin-oxynitride (ITON) thin films have been fabricated by rf-sputtering in plasma containing Ar or a mixture of Ar and N2, respectively. The structural, electrical and optical properties of ITON films were examined and compared with those of ITO films. The microstructure of ITON films was found to be dependent on the nitrogen concentration in the plasma. Increasing the amount of nitrogen in the plasma increased the resistivity and reduced the carrier concentration and mobility of the films. The electrical properties of the ITON films improved after annealing. The absorption edge of the ITON films deposited in pure N2 plasma was shifted towards higher energies and showed reduced infrared reflectance compared to the respective properties of ITO films. The potential of indium–tin-oxynitride films for use as a transparent conductive material for optoelectronic devices is addressed.

Preparation of single phase tungsten carbide by annealing of sputtered tungsten-carbon layers

Abstract Tungsten carbide layers were prepared by sputtering from a stoichiometric WC target and subsequent annealing. Carbide formation was found at temperatures above 800°C. Annealing in pure hydrogen ambient results in a carbon depletion in the layers and the formation of a dominant W 2 C phase. We demonstrate that propane added to the annealing ambient stimulates a transformation of the tungsten-carbon layers to a stoichiometric WC phase. The variation of the propane concentration allows a continuously alteration of the layer structure between single phase WC and a mixed layer with dominant W 2 C and the adjustment of different values of the electrical resistance and the optical constants.

Initial stages in the carbonization of (111)Si by solid-source molecular beam epitaxy

Silicon carbide can be reproducibly grown on (111)Si below 600 °C by carbonization using an elemental solid carbon source in molecular beam epitaxy. The initial stages were observed by in situ reflection high-energy electron diffraction. Prior to silicon carbide growth, the continuous carbon flux lead to a transition from the (7×7) reconstruction of clean (111)Si to a carbon-induced (∛×∛)R30° structure. Above 660 °C, the silicon carbide growth starts directly on the silicon surface via three-dimensional nucleation. Below 660 °C, first a thin silicon–carbon alloy was formed by diffusion of carbon into the surface near the region with a concentration exceeding the bulk solubility in silicon.

Reduced surface electron accumulation at InN films by ozone induced oxidation

A room temperature ozone induced oxidation of thin InN films is proposed to improve the electric transport properties. The sheet carrier density is reduced upon oxidation by a value which is in the order of the electron concentration of an untreated InN surface. Thus, ozone effectively passivates the surface defect states on InN and might be an effective method to prepare InN films for electronic applications. A model for the improved electron transport properties is proposed taking into account the decreased surface band bending and the decreased influence of surface electrons on the net mobility of InN layers.

The role of Si as surfactant and donor in molecular-beam epitaxy of AlN

The growth of Si-doped AlN(0001) thin films on Al2O3(0001) substrates by plasma-induced molecular-beam epitaxy is reported. We have found that Si positively affects the epitaxy being an effective surfactant for AlN growth with a remarkable impact on the crystal quality. It was proven that the characteristic surface reconstruction sequences frequently related to the Al adatoms are obviously Si induced on AlN(0001) surfaces. It was also observed that heavy doping conditions result in volume segregation of Si on the threading dislocation network and in the formation of an amorphous (AlO)(SiO)N cap layer caused by surface oxidation of the accumulated Al and segregated Si. The electron affinity was measured to be smaller than 0.5eV on the clean AlN surface after removing of the cap layer using Ar+ sputtering.

Sputtering effects in hexagonal silicon carbide

Abstract Sputtering yields of α-SiC crystals in the energy range of argon ions from 1 to 2.5 keV as a function of substrate temperature were determined. For a normal incident beam the sputtering yield was in the range 0.45 – 0.71 for acceleration voltages of 1–2.6 keV. The temperature dependence of the sputtering yield was determined at 2 keV in the temperature range 20–1000 °C. A drop in sputtering yield was observed between 400 °C and 700 °C. Auger electron spectroscopy studies and computer simulation of Ar + sputtering as a function of the ion energy at room temperature showed changes in composition under argon sputtering, which were due to preferential sputtering of silicon. At room temperature sputtering led to the formation of a thin amorphized layer on the surface, observed by reflection high energy electron diffraction. At a substrate temperature of 200 °C a partial phase transition of the type GH → 3C was obtained, whereas at 400 °C a partial transition of the type 6H → 15R occurred. At higher substrate temperatures no changes in the polytype structure were observed. However, increasing temperatures led to a decrease and at higher temperatures to elimination of the amorphized fraction at the silicon carbide surface.

Sputtering‐induced surface roughness of polycrystalline Al films and its influence on AES depth profiles

Sputtering-induced surface roughness is the main source of degradation of the depth resolution observed during depth profiling of polycrystalline metals. Atomic force microscopy (AFM) images of polycrystalline Al films at different mean sputtered depths are used to calculate both the depth distribution function (DDF) and the angular distribution function (ADF) of the evolving Al grain surfaces. The shape of the DDF changes with increasing mean sputtered depth, which implies the generation of two different roughness stages during sputtering. However, Auger electron spectroscopy (AES) depth profiling and AFM results show a linear increase of roughness vs. mean sputtered depth in the case of evaporated, polycrystalline Al films. A simple model is developed to calculate the AES intensity for a rough surface. The intensity behaviour as a function of the sputtering time depends on the ADF of microplanes and on the sample tilt angle and generally shows a marked decrease for high tilt angles. The sputtering rate distribution is determined using the DDF. A good fit of the AES depth profile of the Al film requires both the calculated intensity behaviour and the convolution using the DDF, which depends on the sputtering time.

The estimation of sputtering yields for SiC and Si

Abstract Sputtering yields of crystalline silicon carbide and silicon have been determined experimentally for bombardment by Ne+, Ar+ and Xe+ ions in the energy range between 0.5 and 5 keV under 60° sputtering with respect to the surface normal. Sputter crater measurements on SiC and Si and Auger depth profiles of SiC on Si have been carried out in order to determine the sputtering yields. The measurements are compared with Monte Carlo simulations which have been computed by the simulation static codes, TRIM and TRIRS and by the dynamic codes DYTRIRS and T-DYN as well as with the sputter theory. The simulation results depend strongly on the input parameters which are not well known especially for SiC. The TRIM simulation fits the experimental results very well and the differences between the results of the simulation programs are sometimes greater than their difference from experimentally measured sputtering yields.