Nitridation Of GaAs Research Articles

Investigation of N2 plasma GaAs surface passivation efficiency against air exposure: Towards an enhanced diode

GaAs(001) substrates nitrided with N2 plasma at various temperatures were investigated after being exposed to air for 40 days. They were studied by means of parallel angle-resolved X-ray photoelectron spectroscopy, scanning electron microscopy, micro-photoluminescence and time-resolved photoluminescence (TRPL). Several nitrided GaAs Schottky diodes were manufactured to find the optimal nitridation conditions for high diode quality. An improvement on the ideality factor was achieved for a diode with 1.3 nm-thick GaN layer grown at room temperature and crystallized at 620 °C. The crystallization process was needed to enhance the air-exposed GaAs photoluminescence efficiency by a factor 15. TRPL measurements showed a spectacular increase in the decay time (×4), even for a sample exposed to air for 2 years. A high level of GaAs surface chemical protection was achieved. Indeed, neither the element arsenic As0 nor Ga and As oxides states were detected at the GaN/GaAs interface for nitridation at high temperature (500 °C), yielding a 3.1 nm-thick GaN layer. However, for nitridation temperatures above 300 °C, pits with an inversed pyramidal shape and square base were formed at the surface, their size increased as nitridation temperature was raised. These pits acted as non-recombination centers which reduced the GaAs photoluminescence yield.

DFT and experimental FTIR investigations of early stages of (0 0 1) and (1 1 1)B GaAs surface nitridation

The aim of the present work is to perform Attenuated Total Reflectance-Fourier Transform Infra-Red spectroscopy (ATR-FTIR) investigations during N2 plasma treatment of GaAs surfaces at 500 °C inside an UHV chamber using the high intensity light of SOLEIL synchrotron at SMIS beamline. Moreover this work uses the complementarities of Density Functional Theory (DFT) normal-mode frequency calculations with ATR-FTIR measurements to assist in the assignment of vibrations involving bonds to nitrogen atoms, especially by rendering the GaN layer partially amorphous (by removing the crystal symmetry constraint, using Car Parrinello dynamics to simulate annealing in geometry optimization). s and p polarizations were used to study the evolution of the different GaN vibrations during the nitridation of GaAs for two surface orientations (0 0 1) and (1 1 1)B. Results show that normal stretch vibrations are always detected at the same frequency matching the DFT calculated values very well, whereas other vibration modes (bridge symmetric and asymmetric stretches for (0 0 1) GaAs and tripod symmetric and asymmetric stretches for (1 1 1)B GaAs) induced by the non-crystallinity of the GaN layer exhibit variable frequencies. Furthermore evolutions of these frequencies with the nitridation time provide much information on bond creations, especially at the very beginning of the process.

Self‐Induced Nucleation Growth of GaN Columns by Chemical Vapor Deposition

GaN columns are grown by (1 1 1) GaAs nitridation at 1000 °C. GaAs wafers are used as a substrate and Ga source. The nitridation is performed using a hydrogen and ammonia flow mix into a horizontal chemical vapor deposition (CVD) system at atmospheric pressure. XRD in correlation with pole figure shows that the structure is wurtzite with a (0 0 0 2) preferential plane. The SEM images show the growth of GaN columns with an agglomerate formation on top. EDS results show that the agglomerate is Ga rich, suggesting a self‐induced nucleation growth. The growth mechanism is discussed briefly. The average diameter and length of the columns are around 1.2 and 10 µm, respectively. The method reported here do not use a template or foreign metallic particles catalyst.

Characterization of Ar/N2/H2 middle-pressure RF discharge and application of the afterglow region for nitridation of GaAs

This work characterizes the production and destruction of nitrogen and hydrogen atoms in RF capacitively coupled middle-pressure discharge in argon/nitrogen/hydrogen mixtures. Input power, electron concentration, electric field strength and mean electron energy were determined on the basis of electrical measurements. Gas temperature and concentration of Ar atoms in 1s states were determined from spectral measurements. On the basis of experimentally determined plasma characteristics, main production and loss mechanisms of H and N atoms were discussed. The plasma produced radicals were applied for the nitridation and oxide reduction of gallium arsenide in the afterglow region of discharge. After plasma treatment the GaAs samples were analyzed using x-ray photoelectron spectroscopy (XPS) technique. Successful nitridation of GaAs sample was obtained in the case of Ar/5% N2 discharge. In this gas mixture the N atoms were generated via dissociative recombination of created by charge transfer from Ar+. The treatment in Ar/5% N2/1% H2 mixture resulted in the reduction of oxide signals in the XPS spectra. Negligible formation of GaN in the latter mixture was connected with reduced concentration of N atoms, which was, in turn, due to less efficient mechanism of N atom production (electron impact dissociation of N2 molecules) and additional loss channel in reaction with H2.

Combined angle-resolved X-ray photoelectron spectroscopy, density functional theory and kinetic study of nitridation of gallium arsenide

The high density of interface and surface states that cause the strong Fermi pinning observed on GaAs surfaces can be reduced by depositing GaN ultra-thin films on GaAs. To further improve this passivation, it is necessary to investigate the nitridation phenomena by identifying the distinct steps occurring during the process and to understand and quantify the growth kinetics of GaAs nitridation under different conditions. Nitridation of the cleaned GaAs substrate was performed using N2 plasma source. Two approaches have been combined. Firstly, an AR-XPS (Angle Resolved X-ray Photoelectron Spectroscopy) study is carried out to determine the chemical environments of the Ga, As and N atoms and the composition depth profile of the GaN thin film which allow us to summarize the nitridation process in three steps. Moreover, the temperature and time treatment have been investigated and show a significant impact on the formation of the GaN layer. The second approach is a refined growth kinetic model which better describes the GaN growth as a function of the nitridation time. This model clarifies the exchange mechanism of arsenic with nitrogen atoms at the GaN/GaAs interface and the phenomenon of quasi-saturation of the process observed experimentally.

Electronic and Spectroscopic Study of the GaAs nitridation – Electronic Characterization Associated

Gallium nitride is one of the III-V semiconductors the most promising in many application areas. Indeed, because of its large direct bandgap (3,4 eV), it can be dedicated to both optoelectronic applications as transistors achieve hyper frequency. It allows the manufacture of components stable at high temperatures and high frequencies. In this work we are interested in the nitriding of gallium arsenide substrates of n-type in order to obtain a thin layer of GaN. The samples were chemically cleaned immediately introduced into the chamber ultra-high vacuum. They then undergo ionic cleaning in situ by argon ions. Spectrometric analyzes do show the absence of any impurities from the surface, in fact, it only detects the presence of gallium and arsenic. Before proceeding to the nitriding of our structures, deposition of gallium is conducted for 20 minutes to send then simultaneously nitrogen and gallium. Analyzes were performed elaborate structures using X-ray photoelectron spectroscopy (XPS). Deposition of mercury (Hg) has been developed on the structures, we have then made an electrical characterization I-V to see the effect of nitriding on the resulting structure.

Real Time Infra-Red Absorption Analysis of Nitridation of GaAs(001) by Hydrazine Solutions

The chemical bonds established on GaAs(001) by wet nitridation in hydrazine solutions containing 0.01 M of sodium sulfide are investigated using in-situ IR absorption spectroscopy. Hydrazine distillation is found to be necessary in order to avoid numerous carbon-related features in the spectra. The absorption spectrum consists of positive lines due to adsorbed hydrazine molecules and of negative lines due to water being removed from the surface. Well-defined structures near 960 cm−1 and 1020 cm−1 as well as a broader line near 1008 cm−1, not present in the absorption spectrum of the solution, also appear. Investigation of isotopic effects, of the effect of plasma nitridation and of the kinetics of the various lines suggests that hydrazine bonding first occurs to surface Ga atoms in a singly-bonded (Ga-NH-NH2) and doubly-bonded GaGa > N − NH2 end-on configuration. At a later stage, dissociative interaction between chemisorbed hydrazine molecules forms the GaGa > NH configuration.

Effects of substrate nitridation and buffer layer on the crystalline improvements of semi-polar InN(101¯3) crystal on GaAs(110) by MOVPE

In this report, effects of ammonia nitridation and low temperature InN buffer growth were investigated to improve the crystalline quality of InN(101¯3) grown on GaAs(110) by metalorganic vapor phase epitaxy (MOVPE). InN(101¯3) single crystal including less than 0.1% of differently oriented domains was successfully grown by inserting low temperature InN buffer layer. The full width at half maximum (FWHM) values of InN(101¯3) epitaxial layer were drastically decreased from 89arcmin to 55arcmin after processing ammonia nitridation of GaAs(110) substrate surface. Furthermore, the FWHM value was decreased to 38arcmin by increasing growth time, and the mechanism of dislocation annihilation happened during epitaxial growth was discussed.

Cubic GaN layers grown by metalorganic chemical vapor deposition on GaN templates obtained by nitridation of GaAs

Cubic gallium nitride epitaxial layers were grown by metalorganic chemical vapor deposition on GaN templates obtained by nitridation of GaAs substrates. The GaN structure can be peeled off the GaAs substrate and it can be handled separately. X-ray diffraction, Raman and photoluminescence measurements show that the epitaxial layers are cubic and monocrystalline.

Chemistry of Wet Treatment of GaAs(111)B and GaAs(111)A in Hydrazine-Sulfide Solutions

Chemical treatment by hydrazine-sulfide solutions, known to produce surface nitridation of GaAs(100), was applied to GaAs(111)A and B surfaces. The chemistries of these treatments for the Ga-terminated A surface and the As-terminated B one were investigated using synchrotron radiation photoemission and Auger electron spectroscopies. For the B surface, such treatment was found to produce an effective surface nitridation, via substitution of surface arsenic with nitrogen atoms from hydrazine molecules. The process automatically stops after formation of one monolayer. In contrast, the A surface is covered by sulfur bonded to underlying gallium. This extreme dependence on surface polarity is explained by competitive adsorption processes of and anions and of hydrazine molecules, on Ga-adsorption sites, which have distinct configurations on the A and B surfaces.

Formation of GaAs 1− xN x nanofilm on GaAs by low energy N 2+ implantation

Nitridation of GaAs (1 0 0) by N 2 + ions with energy E i = 2500 eV has been studied by Auger- and Electron Energy Loss Spectroscopy under experimental conditions, when electrons ejected only by nitrated layer, without contribution of GaAs substrate, were collected. Diagnostics for quantitative chemical analysis of the nitrated layers has been developed using the values of NKVV Auger energies in GaN and GaAsN chemical phases measured in one experiment, with the accuracy being sufficient for separating their contributions into the experimental spectrum. The conducted analysis has shown that nanofilm with the thickness of about 4 nm was fabricated, consisting mainly of dilute alloy GaAs 1− x N x with high concentration of nitrogen x ∼ 0.09, although the major part of the implanted nitrogen atoms are contained in GaN inclusions. It was assumed that secondary ion cascades generated by implanted ions play an important role in forming nitrogen-rich alloy.

Nitrogen Ion Induced 2D-GaN Layer Formation of GaAs (001) Surface

This study demonstrates the formation of two-dimensional GaN on GaAs (001) surface by bombardment of nitrogen ions at room temperature. In this work the ion induced nitridation of GaAs (001) surface using nitrogen ion beam of different energies (range from 250 eV to 5 keV) has been investigated using in-situ X-ray Photoelectron Spectroscopy (XPS). A Ga rich surface produced by Art ion etching, promotes initial nitridation. Using nitrogen ion of different energies of constant fluence performs the nitridation. The nitridation suggests that the degree of nitridation increase as the nitrogen ion energy increases up to 3 keV and then attains saturation. The core level and valance band spectra were monitored to observe the chemical and electronic changes as a function of nitrogen ion beam energy. It is observed that Ga(3d) core level peak shifts during nitridation and N(1s) core level spectra shows that the intensity of the nitrogen peak increases and the Ga (LMM) auger peak shifts towards the higher binding energy, reveal the forming of N bonds with Ga by replacing the Ga-As bonds, forming GaN.

XPS investigation of ion beam induced conversion of GaAs(0 0 1) surface into GaN overlayer

For the advance of GaN based optoelectronic devices, one of the major barriers has been the high defect density in GaN thin films, due to lattice parameter and thermal expansion incompatibility with conventional substrates. Of late, efforts are focused in fine tuning epitaxial growth and in search for a low temperature method of forming low defect GaN with zincblende structure, by a method compatible to the molecular beam epitaxy process. In principle, to grow zincblende GaN the substrate should have four-fold symmetry and thus zincblende GaN has been prepared on several substrates including Si, 3C–SiC, GaP, MgO, and on GaAs(0 0 1). The iso-structure and a common shared element make the epitaxial growth of GaN on GaAs(0 0 1) feasible and useful. In this study ion-induced conversion of GaAs(0 0 1) surface into GaN at room temperature is optimized. At the outset a Ga-rich surface is formed by Ar + ion bombardment. Nitrogen ion bombardment of the Ga-rich GaAs surface is performed by using 2–4 keV energy and fluence ranging from 3 × 10 13 ions/cm 2 to 1 × 10 18 ions/cm 2. Formation of surface GaN is manifested as chemical shift. In situ core level and true secondary electron emission spectra by X-ray photoelectron spectroscopy are monitored to observe the chemical and electronic property changes. Using XPS line shape analysis by deconvolution into chemical state, we report that 3 keV N 2 + ions and 7.2 × 10 17 ions/cm 2 are the optimal energy and fluence, respectively, for the nitridation of GaAs(0 0 1) surface at room temperature. The measurement of electron emission of the interface shows the dependence of work function to the chemical composition of the interface. Depth profile study by using Ar + ion sputtering, shows that a stoichiometric GaN of 1 nm thickness forms on the surface. This, room temperature and molecular beam epitaxy compatible, method of forming GaN temperature can serve as an excellent template for growing low defect GaN epitaxial overlayers.

Capacitance-voltage and photoluminescence study of high-k∕GaAs interfaces controlled by Si interface control layer

The authors performed a detailed capacitance-voltage (C-V) and photoluminescence (PL) study of the high-k dielectric/GaAs interface controlled by the Si interface control layer (Si ICL) grown by molecular beam epitaxy to investigate the feasibility of a PL method for interface characterization and to find out the optimum thickness of the Si ICL. The sample had a HfO2∕SiNx∕Si ICL/n-GaAs structure where the ultrathin SiNx buffer layer was formed by in situ partial nitridation of the Si ICL itself. For this structure, they measured the quantum efficiency of photoluminescence as a function of the excitation photon flux density and carried out a computer analysis to determine the most likely distribution of the interface state density Dit. Remarkably good agreements were obtained between the high-frequency C-V method and the PL method, indicating that the present PL method may serve as a powerful contactless and nondestructive tool for developing an optimal surface passivation structure and its processing technology. Using C-V and PL methods, they found the optimum initial thickness of Si ICL before partial nitridation to be 5–6 ML. With this thickness, a Dit minimum value of (1–2)×1011cm−2eV−1 was achieved in the HfO2∕SiNx∕Si ICL/n-GaAs structure. When the thickness was too large, it led to the generation of misfit dislocations, whereas a too thin Si ICL led to subcutaneous nitridation of GaAs during partial nitridation of the Si ICL, leading to interface disorder.

XPS study of the formation of ultrathin GaN film on GaAs(1 0 0)

The nitridation of GaAs(1 0 0) surfaces has been studied using XPS spectroscopy, one of the best surface sensitive techniques. A glow discharge cell was used to produce a continuous plasma with a majority of N atomic species. We used the Ga3d and As3d core levels to monitor the chemical state of the surface and the coverage of the species. A theoretical model based on stacked layers allows to determine the optimal temperature of nitridation. Moreover, this model permits the determination of the thickness of the GaN layer. Varying time of nitridation from 10 min to 1 h, it is possible to obtain GaN layers with a thickness between 0.5 nm and 3 nm.

Soft nitridation of GaAs(100) by hydrazine sulfide solutions: Effect on surface recombination and surface barrier

The effect of nitridation of GaAs(100) by hydrazine sulfide solutions on the surface recombination velocity and surface barrier has been studied using photoluminescence and photoreflectance spectroscopies. Nitridation produces a decrease of surface recombination velocity by a factor of 26. After three years of air exposure, the recombination velocity is still smaller than for the naturally oxidized surface by a factor of 11. The observed effect is caused by a continuous nitride monolayer bonded with the GaAs substrate. The surface Fermi level is still pinned near midgap, which is attributed to residual unpassivated surface defects.

Wet chemical nitridation of GaAs(001) surface

Auger Electron Spectroscopy and Scanning Tunnelling Microscopy were used to study the chemical and structural properties of the GaAs(001) surface after wet chemical nitridation by hydrazine-sulfide solutions. AES results show that the as-nitrided surface is covered by a thin film formed by a layer of nitrogen atoms strongly bonded with the substrate, and by a layer of residual impurities above it. The residual layer consists of oxygen- and sulfur-containing compounds, which are removed by annealing at near 450 and 520°C respectively. The STM relief of the annealed surface is smooth with the rms roughness of the order of 0.4 nm. It is formed by numerous grain-like features of average lateral size near 5 nm and of 0.5 nm of height. Possible origin of the features is discussed.

Nitridation of porous GaAs by an ECR ammonia plasma

The effect of surface porosity of GaAs on the nature of growth of GaN, by use of plasma nitridation of GaAs, has been investigated. Porous GaAs samples were prepared by anodic etching of n-type (110) GaAs wafers in HCl solution. Nitridation of porous GaAs samples were carried out by using an electron–cyclotron resonance-induced ammonia plasma. The formation of mixed phases of GaN was investigated using the grazing angle x-ray diffraction method. A remarkable improvement in the intensity of photoluminescence (PL) compared with that of GaN synthesized by direct nitriding of GaAs surface has been observed. The PL intensity of nitrided porous GaAs at the temperature of 380 °C was found to be about two orders of magnitude higher as compared with the directly nitrided GaAs at the temperature of 500 °C. The changes in the morphology of nitrided porous GaAs have been investigated using both scanning electron microscopy and atomic force microscopy.

Nitrogen–arsenic exchange processes and investigation of the nitrided GaAs surfaces in MOVPE

We studied nitrided surfaces and the kinetics of nitridation with tertiarybutylhydrazine (tBHy) in metal organic vapor-phase epitaxy (MOVPE). Reflectance anisotropy spectroscopy (RAS) and X-ray diffraction (XRD) were used for in situ and ex situ analysis. By comparing RAS spectra with molecular beam epitaxy (MBE) results we found a ( 3 × 3 ) -like reconstruction of the nitrided surfaces. The kinetics of the nitrogen–arsenic exchange were studied by RAS transients. An activation energy of E a ≃ 1.7 eV was calculated for the exchange process. This value was independent from the tBHy partial pressure. Incorporation of nitrogen into GaAs up to six monolayers was further demonstrated by ex situ XRD for samples grown between 460 and 560 ∘ C .

Surface modification of GaAs during argon ionic cleaning and nitridation: EELS, EPES and XPS studies

Abstract The cleaning and the nitridation of GaAs(1 0 0) substrates have been studied in this work by electron energy loss spectroscopy (EELS), elastic peak electron spectroscopy (EPES) and X-ray photoelectron spectroscopy (XPS). The nitridation of GaAs(1 0 0) was performed using a double differential pumping RF cell. We have studied in a first part, the surface modifications of the substrate during ionic cleaning. In a second part, we have determined the λ i ( E ) K ( E , E n ) curves from EELS spectra using Tougaard's procedure for cleaned-GaAs(1 0 0) and nitrited-GaAs(1 0 0) substrates. The thickness of the GaN overlayer was deduced from these results.