Sputtering Of GaAs Research Articles

Investigation of the process of reactive ion-beam sputtering of gallium arsenide using optical emission spectroscopy

The aim of this work was to study the process of reactive ion-beam sputtering of gallium arsenide using optical emission analysis of plasma in the target region to determine the optimal conditions for the formation of intrinsic GaAs oxides. The ion source was a plasmatron based on an anode layer accelerator (UAS), which generated a stream of accelerated argon and oxygen ions with an energy of 400–1200 eV. The target was made from tellurium doped gallium arsenide. Intense GaI lines (2874.2 Å, 2943.6 Å, 4033.0 Å and 4172.1 Å), atomic argon ArI, argon ions, and also FeI lines were detected in the spectrum upon sputtering of GaAs by Ar+ ions. The appearance of iron lines can be explained by the sputtering of the pole tips of the magnetic system of the ion source. An increase in the accelerating voltage from 1 to 3 kV leads to an increase in the intensity of the peaks of atomic gallium GaI (4172.1 Å) by 2.38 times, the GaI line (4033.0 Å) by 3.25 times, the GaI line (2943.6 Å) 3.4 times, GaI lines (2874.2 Å) 5 times. It was found that an increase in the partial pressure of oxygen leads to a sharp decrease in the peaks of GaI (4033.0 Å) and GaI (4172.1 Å) due to the chemical interaction of gallium and oxygen. Sputtering in pure oxygen reduces the intensity of these peaks by 8 and 5 times, respectively. The intensities of the peaks of atomic gallium GaI (2874.2 Å) and GaI (2943.6 Å) decreased in 2 and 1.78 times, respectively. In the presence of a positive potential on the target, the intensity of all lines of atomic gallium monotonically decreases with increasing potential. In the emission spectrum, lines of atomic oxygen OI (7774.2 Å) and molecular positive ions O+2 (6418.7 Å, 6026.4 Å, 5631.9 Å and 5295.7 Å) were detected. In the presence of a positive potential on the target, a monotonic decrease in the intensity of the above oxygen lines was observed. This indicates an intensification of chemical interaction of oxygen with target elements and, accordingly, a decrease in the free active oxygen particles.

Gallium nitride films of high n-type conductivity grown by reactive sputtering

The origin of n-type conductivity in as grown, undoped GaN has been debated over several decades, with contradictory views. This work deals with reactively sputtered, undoped GaN films in which a large decrease of resistivity from ∼105 to ∼2 × 10−3 Ω cm is seen, as the nitrogen percentage in argon–nitrogen sputtering atmosphere is decreased from 100% to 10%, resulting in high electron concentration ∼1020 cm−3 at the lower end of nitrogen pressure. The electrical behavior of these films has been correlated with their composition and chemical state to understand the nature of point defects which influence n-type conductivity. Powder x-ray diffraction and phi scans of the undoped GaN films grown by sputtering of GaAs at 700 °C on c-sapphire reveal epitaxial growth of single phase GaN. SIMS results show the absence of arsenic in the films and uniformly distributed gallium and nitrogen along with oxygen impurity, across their thickness. XPS data reveal the decrease of N/Ga ratio, as the nitrogen partial pressure is decreased along with the increase of uncoordinated Ga, indicating the formation of nitrogen vacancies. In the high resistivity films grown at higher nitrogen percentage in sputtering atmosphere, oxygen impurities appear to be primarily responsible for creation of n-type carriers, which are compensated by Ga vacancies and possibly VGa–ON complexes. The drastic enhancement of n-type conductivity and carrier concentration in the low resistivity films grown at lower nitrogen percentage, which reveal significantly smaller nitrogen content, is attributed dominantly to the increase in nitrogen vacancies and uncoordinated Ga.

Formation of nearly defect-free nanoripples by sputtering of GaAs (001) surface at high temperature

The evolution of GaAs (001) surface morphology by normal incidence 1 keV Ar+ ion sputtering at high temperature has been investigated for different temperature and ion fluence. An anisotropic surface modulation is observed above the substrate recrystallization temperature ∼300 °C. With increase of sputtering time, they evolve into highly ordered and almost defect-free ripple-like structure consisting of alternate arrays of elongated terraces and nano-grooves with ridges along the <11¯0> direction. Such surface instability is attributed to the effect of anisotropic surface diffusion of vacancies in the presence of Ehrlich–Schwoebel barrier. The amplitude and wavelength of the ripple show a power law increase with sputtering time and finally saturate at longer time irradiation.

Heterojunction Diodes and Solar Cells Fabricated by Sputtering of GaAs on Single Crystalline Si

This work reports fabrication details of heterojunction diodes and solar cells obtained by sputter deposition of amorphous GaAs on p-doped single crystalline Si. The effects of two additional process steps were investigated: A hydrofluoric acid (HF) etching treatment of the Si substrate prior to the GaAs sputter deposition and a subsequent annealing treatment of the complete layered system. A transmission electron microscopy (TEM) exploration of the interface reveals the formation of a few nanometer thick SiO2 interface layer and some crystallinity degree of the GaAs layer close to the interface. It was shown that an additional HF etching treatment of the Si substrate improves the short circuit current and degrades the open circuit voltage of the solar cells. Furthermore, an additional thermal annealing step was performed on some selected samples before and after the deposition of an indium tin oxide (ITO) film on top of the a-GaAs layer. It was found that the occurrence of surface related defects is reduced in case of a heat treatment performed after the deposition of the ITO layer, which also results in a reduction of the dark saturation current density and resistive losses.

Sputtering of GaAs under oblique Cs bombardment: A simulation study

Sputtering of GaAs under oblique 2–10 keV Cs ion bombardment is studied by means of computer simulation as applied to the experimental data by Verdeil et al. published recently. Special attention is given to the angular distribution of sputtered atoms in the steady-state limit and to the relevant concentrations of surface Ga and As atoms, S Ga and S As, respectively. The best-fit values of S Ga and S As found in simulations favor segregation of As. A very pronounced effect of resputtering of atoms deposited on a collector of sputtered matter is noted. For forecasting purposes, the sputtering of GaAs under oblique bombardment with 0.1–1 keV Cs ions is also shortly considered.

Experimental studies of ionization processes in sputtering of GaAs

Ionization processes in GaAs have been analyzed using primary ion beams (He +, Xe +) and primary neutral beams (He 0, Xe 0) with energies between 500 eV and 4 keV. The ionization probability of Ga + has been found to be independent of bombarding conditions and equal to 0.04. The As + and As − ionization yields depend very strongly on the bombarding conditions, and are the same for both ion and neutral particle bombardments. The absolute ionization probability of As + for Xe impact changes from 8 × 10 −7 to 2 × 10 −5 when the primary beam energy changes from 500 eV to 4 keV. Taking these experimental results into account, the most probable ionization process for As is suggested and discussed.

Vacancy kinetics and sputtering of GaAs(110).

Bombardment of GaAs(110) at 300\ensuremath{\le}T\ensuremath{\le}775 K with ${\mathrm{Ar}}^{+}$ ions at normal incidence creates surface-layer defects that generally span one or two unit cells, as shown by scanning tunneling microscopy. Vacancies produced in this way diffuse via thermal activation to form single-layer vacancy islands. The diffusion of divacancies favors [11\ifmmode\bar\else\textasciimacron\fi{}0] and accommodation at islands produces roughly isotropic islands. Modeling of growth showed an overall Arrhenius behavior for diffusion with an activation energy of 1.3\ifmmode\pm\else\textpm\fi{}0.2 eV. Investigations of the surface morphology during multilayer erosion revealed deviation from layer-by-layer removal with scaling exponents between 0.4 and 0.5 for 626\ensuremath{\le}T\ensuremath{\le}775 K.

Bombardment-induced light emission spectroscopy of GaAs

Gal spectral lines originating from the sputtering of GaAs under 6–10 keV Ar + ion bombardment have been studied. Results of the measurements on the target position, beam current and projectile energy dependences of 4172, 4033 and 2944 Å lines are presented. It is found that the secondary photon emission yields can be well described by the model proposed by Wright and Gruen.

Surface roughness development during sputtering of GaAs and InP: Evidence for the role of surface diffusion in ripple formation and sputter cone development

Surface diffusion is shown to be the important factor in sputter–induced ripple and cone development on GaAs and InP surfaces for conditions typical of depth profiling when using surface analysis techniques. Ripple formation has been observed on both GaAs and InP when sputtered using Cs+ and O+2 ion beams. For GaAs, the ripple ‘‘wavelength’’ increases with sample temperature in the range from 45 to 100 °C, in qualitative agreement with the surface diffusion model of Bradley and Harper. No ripple formation is observed when the GaAs sample is cooled to −30 °C where surface diffusion is limited, or heated above 100 °C, where a proposed surface phase change may alter the diffusion rate. Ripple development also occurs on InP, but it is impossible to observe at 100 °C due to extensive cone formation. At this elevated temperature, Ar+ sputtering of InP leads to a surface enrichment of indium that is accompanied by a change in the In M4,5N4,5N4,5 Auger line shape toward that for indium metal. This result, together with the observation that cone formation is eliminated for sputtering at −20 °C, supports the intrinsic model where sputtering causes indium enrichment and surface diffusion that results in the agglomeration of indium metal into clusters. These clusters produce cone formation, possibly through the difference in sputter rates of indium and InP.

The sputtering of gallium arsenide at elevated temperatures

The energy distribution of atoms and molecules sputtered from a polycrystalline GaAs sample with a 6 keV Ar ion beam have been measured. The temperature of the target ranged from 30°C to 350°C. Total sputtering yield of the investigated sample has also been measured. The results clearly show that there is a large contribution of molecular component in the sputtered flux and that the molecular component increases above 250°C in comparison to the atomic components thus yielding an increase in the total sputtering yield, as observed previously by Brozdowska et al. The enhanced molecular component at temperatures above 250°C can be explained by the appearance of a spike effect. The results obtained at low temperature can be explained in terms of the collision cascade mode. There is no contribution of beam-induced thermal vaporization to the sputtering of GaAs.