Treated GaAs Surfaces Research Articles

Impact of GaAs(100) surface preparation on EQE of AZO/Al2O3/p-GaAs photovoltaic structures.

In order to effectively utilize the photovoltaic properties of gallium arsenide, its surface/interface needs to be properly prepared. In the experiments described here we examined eight different paths of GaAs surface treatment (cleaning, etching, passivation) which resulted in different external quantum efficiency (EQE) values of the tested photovoltaic (PV) cells. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) examinations were conducted to obtain structural details of the devices. X-ray photoelectron spectroscopy (XPS) with depth profiling was used to examine interface structure and changes in the elemental content and chemical bonds. The photoluminescence (PL) properties and bandgap measurements of the deposited layers were also reported. The highest EQE value was obtained for the samples initially etched with a citric acid-based etchant and, in the last preparation step, either passivated with ammonium sulfide aqueous solution or treated with ammonium hydroxide solution with no final passivation. Subsequent I–V measurements, however, confirmed that from these samples, only the sulfur-passivated ones provided the highest current density. The tested devices were fabricated by using the ALD method.

Investigation of GaAs surface treatments for ZnSe growth by molecular beam epitaxy without a buffer layer

Atomically clean and smooth surfaces are critical prerequisites for the epitaxial regrowth of dissimilar semiconductors. Using ZnSe/GaAs as a model system, epitaxial regrowth without a buffer layer after thermal cleaning with various As-fluxes, atomic Ga flux, and atomic hydrogen treatments to the GaAs substrates and the surfaces were investigated via in-situ Auger electron spectroscopy. The ZnSe epilayers grown on the pre-treated GaAs surfaces without a buffer layer were characterized by X-ray diffraction, photoluminescence and atomic force microscopy to evaluate the effectiveness of the surface treatment methods. It was found that a high quality ZnSe layer can be achieved by atomic hydrogen surface treatment at 300 °C without requiring GaAs buffer layer growth, which reveals a path for epitaxy growth avoiding high temperature treatments.

Application of the Atomic Layer Etching technique to remove broken layers after plasma-etched GaAs surface treatment

The work considers the application of focused ion beam techniques for the formation of nanoscale structures, as well as the atomic layer etching method for removing layers with surface defects. Also in the work, modeling of the formation of structures by the FIB method on the GaAs surface was used to determine the depth of penetration of atoms into the structure under certain experimental conditions. This method of forming defect-free structures was developed for the formation of a nanoscale surface relief for the subsequent growth of quantum dots by the method of drop molecular beam epitaxial.

Effects of GaAs Surface Treatment Processes on Photocurrent Properties of Cs/p-GaAs (001) Fabricated Using a MOCVD–NEA Multichamber System

The effects of surface treatment processes of p-GaAs (001) on the photocurrent properties of Cs/p-GaAs (001) obtained during Cs evaporation have been investigated using a metal–organic chemical vapor deposition (MOCVD)–negative electron affinity (NEA) multichamber system comprising an MOCVD chamber, load–lock chamber, and NEA surface-activation chamber. Samples were transferred from the MOCVD chamber to the NEA surface-activation chamber without air exposure. Moreover, the air exposure time before Cs evaporation was controlled by opening the load–lock chamber. Almost the same peak photocurrents were observed for samples fabricated using only tertiarybutylarsine or H2 supply after thermal cleaning of the p-GaAs substrate. However, tertiarybutylphosphine supply after thermal cleaning of the p-GaAs substrate degraded its surface morphology and decreased its peak photocurrent. The peak photocurrent decreased monotonically with lengthening air exposure time. Moreover, the start time of the rise in photocurrent was delayed monotonically with lengthening air exposure time. These experimental results reveal that the surface treatment process of p-GaAs (001) applied before Cs evaporation is an important factor controlling the photocurrent properties.

Molecular beam epitaxy of SrTiO3 on GaAs(001): GaAs surface treatment and structural characterization of the oxide layer

Epitaxial SrTiO3 (STO) layers were grown on GaAs(001) substrates by molecular beam epitaxy. A Ti-based surface passivation was used prior to STO growth. The different steps of this passivation procedure are discussed on the basis of reflection high energy electron diffraction experiments. We also show that the STO/GaAs template presents an excellent structural quality with a flat surface, an abrupt semiconductor/oxide interface, and a good crystallinity. Such STO/GaAs templates open perspectives for the integration of perovskite oxides on semiconductor substrates.

Properties of LaAlO3 thin film on GaAs(1 0 0) treated by in situ NH3 plasma

In this work, we deposited LaAlO3 film on n-type GaAs by plasma enhanced atomic layer deposition (PEALD). In situ NH3 plasma nitridation of the GaAs surface was introduced to control the interface prior to plasma enhanced atomic layer deposition of LaAlO3. The chemical bonding state of NH3 plasma treated GaAs surface were investigated by X-ray photoelectron spectroscopy (XPS), which indicate that NH3 plasma nitridation can suppress interfacial growth on GaAs substrate. Transmission electron microscopy (TEM) images show the interface between LaAlO3 and GaAs was smooth and there was not obvious interface layer observed. The capacitance–voltage (C–V) and leakage current density–voltage (J–V) measurement indicate that the NH3 plasma nitridation improved the electrical properties of LaAlO3 films on GaAs substrate.

Interfacial Characteristics for LaAlO<sub>3 </sub>Gate Dielectric on S Passivated GaAs Substrate

In this work, we present the results of an investigation into the effectiveness of varying ammonium sulphide (NH4)2S concentrations in the passivation of n-type GaAs. Samples were degreased and immersed in aqueous (NH4)2S solutions of concentrations 22% and 10%for 10 min at 295 K, immediately prior to plasma enhanced atomic layer deposition of LaAlO3. The chemical bonding state of (NH4)2S treated GaAs surface were investigated by X-ray photoelectron spectroscopy (XPS), which indicate that Sulfur passivation can reduce intrerfacial GaAs-oxide formation. Transmission electron microscopy (TEM) was implemented to characterize the interface morphology. Finally, capacitance-voltage (C-V) and leakage current density-voltage (J-V) measurement were used to characterize the electrical properties of LaAlO3 films.

In situ surface pre-treatment study of GaAs and In0.53Ga0.47As

The impact of using multiple cycles of trimethyl-aluminum (TMA) prior to Al2O3 deposition on the properties of (NH4)2S treated In0.53Ga0.47As and GaAs substrates was investigated by in situ x-ray photoelectron spectroscopy. Increasing the number of TMA cycles prior to Al2O3 atomic layer deposition (ALD) was seen to decrease the concentration of As-As detected at the oxide-semiconductor interface. The impact of annealing the (NH4)2S treated GaAs surface in situ prior to ALD, in various environments, was also investigated.

The fabrication of nanomesas and nanometal contacts by using atomic force microscopy lithography

The influence of preoxidation GaAs surface treatment over the atomic force microscopy-induced local anodic oxidation (LAO) is investigated in this paper. By immerging the GaAs samples into NaOH aqueous solutions, higher nano-oxides with better height distribution could be observed after LAO. The phenomenon is attributed to the hydrophilic surfaces obtained after the treatment such that higher local humidity and uniform water molecular distribution would be obtained on the GaAs surfaces, by using the higher nano-oxides with better height uniformity, nanomesas by using wet chemical etching, and nanometal contact after oxide lift-off are fabricated.

Investigation of Sulfur Passivation Treatments for Direct Wafer Bonding of III-V Materials

Bonding techniques for direct wafer bonding of III-V materials by various sulfur passivation treatments are presented. A dry sulfur passivation method utilizing elemental sulfur vapor activated by ultraviolet light in high vacuum is adapted for use in wafer bonding. Large area bonding is achieved for GaAs/GaAs and InP/InP with bulk fracture strength achieved after annealing at 400 °C and 300 °C respectively without large compressive forces. X-ray photoelectron spectroscopy measurements of the treated GaAs surface show the reduction of oxide and creation of sulfide bonds prior to bonding. The electrical conductivity across a sulfur bonded GaAs/GaAs interface is greatly improved with a short anneal (1-2 minutes) at elevated temperatures (500-600 °C) and HRTEM images reveal the interface is restructuring at lower temperatures than reported for other bonding techniques.

HfO 2 – GaAs metal-oxide-semiconductor capacitor using dimethylaluminumhydride-derived aluminum oxynitride interfacial passivation layer

In this letter, treatment of GaAs surface by using dimethylaluminumhydride-derived AlON passivation layer prior to HfO2 deposition is proposed to solve the issue of Fermi level pinning. It has been found that AlON passivation layer effectively suppresses the oxides formation and leads to the Fermi level unpinning at the interface between GaAs and HfO2. Based on analysis from metal-oxide-semiconductor capacitors of Au/HfO2/AlON/GaAs stack, excellent capacitance-voltage characteristics with saturated accumulation capacitance and reduced leakage current have been achieved, which may originate from the decrease in the interface state density and the increase in the conduction band offset.

Influence of gallium arsenide surface treatment in selenium vapors on subsurface defects

Influence of GaAs surface treatment in selenium vapors on the parameters of electronic states in the subsurface GaAs regions is investigated by the methods of volt-ampere and volt-farad characteristics and isothermal capacitance relaxation at temperatures in the interval 77–400 K. Electrophysical measurements of the Schottky barriers formed on the GaAs surface treated in selenium indicate a decrease in the surface electron state (SES) density and unfastening of the Fermi energy level. In this case, generation of subsurface defects is observed that causes compensation of shallow donors and refastening of the Fermi energy level typical of some structures.

Band offsets of atomic-layer-deposited Al2O3 on GaAs and the effects of surface treatment

The metal gate/high-k dielectric/III-V semiconductor band alignment is one of the most technologically important parameters. We report the band offsets of the Al/Al2O3/GaAs structure and the effect of GaAs surface treatment. The energy barrier at the Al2O3 and sulfur-passivated GaAs interface is found to be 3.0±0.1 eV whereas for the unpassivated or NH4OH-treated GaAs is 3.6 eV. At the Al/Al2O3 interface, all samples yield the same barrier height of 2.9±0.2 eV. With a band gap of 6.4±0.05 eV for Al2O3, the band alignments at both Al2O3 interfaces are established.

Effect of GaAs Surface Treatments on Lanthanum Silicate High-K Dielectric Gate Stack Properties

ABSTRACTThe properties of lanthanum silicate (LaSiOx) gate stacks on GaAs substrates have been examined, comparing different GaAs pretreatments; namely a) as-received, b) HCl-treated, and c) sulphur-treated. X-ray photoelectron spectroscopy of the As 3d, Ga 3d, and Ga 2p binding energy peaks were used to reveal the chemical nature of the stacks. After a 400 °C in situ anneal in 10−6 torr pO2, the LaSiOx chemically reduces the As oxides from the as-received GaAs, while Ga oxide species remain. HCl and S-treated GaAs similarly show no As oxides, and a much smaller degree of Ga oxides than the as-received case. The Ga-S bonding may be responsible for lowering the tendency towards Ga oxidation for the S-treated case. On p-type, Zn-doped GaAs, 3.0 nm lanthanum silicate films produce MOS device EOT values of 2.38 nm, 1.51 nm, and 1.37 nm, on as-received, HCl-treated, and S-treated substrates, respectively. The high EOT for the as-received GaAs corresponds to the thicker Ga oxide and elemental As at the interface. The decreases in both Ga oxide and elemental As at the interface of the S-treated stack appears to be related to it having the lowest EOT devices.

Surface treatment for enhancing current gain of AlGaAs/GaAs heterojunction bipolar transistor

This paper presents a method of surface treatment for improving the current gain of an AlGaAs/GaAs heterojunction bipolar transistor (HBT). Several recipes for GaAs surface treatment, including each and several combinations of the H 2 plasma, NH 3 plasma, and (NH 4) 2S x chemical treatments are examined. The lowest SiO 2/GaAs interface state density of 1.23 × 10 10 cm −2 eV −1 is obtained when the GaAs surface is treated in sequence with (NH 4) 2S x :H 2O=1:1 solution, H 2 plasma, and NH 3 plasma. The current gain of an AlGaAs/GaAs HBT, whose extrinsic base surface is treated with this recipe, is enhanced at a low collector current by a factor of 2.5 from that without surface treatment. The maximum current gain is also enhanced by a factor of 1.37.

Two constant phase element behaviour of the admittance characteristics of GaAs metal-insulator-semiconductor structure with deep traps

The capacitance and the conductance vs. the frequency characteristics of Au/Pd/Ti–SiO 2–(n) GaAs structures with and without (NH 4) 2S x treated GaAs surface have been investigated. For normalized conductance G m/ ω characteristics, the peaks with the position dependent on the gate voltage have been observed for both types of structures and also the peaks with the position not dependent on the bias for the (NH 4) 2S x treated samples. That behaviour has been attributed to the interface state contribution and the deep trap contribution, respectively. The equivalent circuit has been presented which allows for the description of the observed admittance peculiarities in a simple way. It contains: the insulator capacitance, the series resistance, the space charge capacitance and the two parallel branches including the constant phase elements (CPE1 and CPE2) connected in series with resistances. The values of parameters of the equivalent circuit elements at different gate voltages have been determined. These elements are attributed to the physical phenomena in different regions of the analysed system. The CPE1 (with parameter n 1 ∼0.54) connected in series with resistance describes the electron processes in the SiO 2-GaAs region leading to the frequency dispersion of the electrical characteristics of the investigated structures in the frequency range which depends on the bias, while CPE2 (with parameter n 2 ∼0.89–0.95) connected in series with resistance models the deep traps admittance.

Low-energy particle treatment of GaAs surface

Modification of high-doped GaAs surface by the interaction with RF plasma and a monoenergetic beam of similar chemical composition (Ar with a low content of H 2) was investigated via the evolution of optical, electrical and structural properties. A reduction in the free charge concentration in the GaAs surface region of ∼100 nm in thickness is concluded from Raman spectroscopy. In the processed samples, the surface electric field strength induced by a laser beam (photoreflectance technique) continually decreases with both the energy and fluence of impinging particles. The same results were obtained by evaluation of quasistatic C– V curves of corresponding MOS structures. They confirmed that longer exposure caused the formation of ∼100-nm-thick modified near-surface region with a decreased donor concentration. After the plasma irradiation, an ∼10-nm-thick outermost insulating layer was created in situ. The formation of textured polycrystalline grains with (100) orientation in the surface region was observed by X-ray diffraction.

Characterization of Pure Water-Treated GaAs Surfaces by Measuring Contact Angles of Water Droplets

A GaAs surface treated with pure water was characterized by using contact angle measurement, Auger electron spectroscopy, and atomic force microscopy. The contact angle was found to be dependent on treatment conditions such as treatment time, agitation of pure water, dissolved oxygen concentration in pure water, and illumination. The contact angle of a water droplet on GaAs surface treated with agitated deionized pure water was found to increase with increasing treatment time, indicating that the hydrophobicity of the surface increased. The agitation of pure water strongly influenced the oxygen concentration and the roughness of the treated GaAs surface, and hence, the contact angle of a water droplet on it. © 2001 The Electrochemical Society. All rights reserved.

Investigation on the surface characteristics of GaAs after sulfuric-vapor treatment

The chemical bonding state and surface morphology of sulfuric-vapor treated GaAs surface were investigated using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The sulfuric vapor was obtained through the heating of (NH4)2Sx solution at 60°C. At the initial state of the treatment, the decrease of elemental As and the generation of As–S bonds were observed. Even after all of the elemental As converted into As–S bonds, peak area of the As–S bond increased until 5 min exposure. Unlike the liquid-phase treatment, the dissolution of the elemental As did not happen during the treatment and the formation of As-polysulfides was observed. Through the surface treatment of the GaAs using sulfuric vapor, small particles were formed and increased with treatment time. After 5 min exposure, they were linked to form a large agglomerate. This corresponds to a deposit of polysulfides containing hydrogen. To evaluate the effectiveness of the sulfuric vapor-treatment against oxidation in air, the treated GaAs was exposed to air and compared with the GaAs treated using a (NH4)2Sx solution. The As-polysulfides and polysulfides containing hydrogen were revealed to be easily decomposed by exposure to air. The character of S bond with GaAs was revealed to be the most important to obtain a passivation effect.

Electrical properties of SiO2–(n) GaAs interface on the basis of measurements of MIS structure capacitance and conductance

The Au/Pd/Ti–SiO2–GaAs structures with PECVD deposited insulator layers have been investigated. The (100) oriented n-GaAs wafers with and without (NH4)2S surface treatments have been used. The measurements of capacitance–voltage characteristics at different frequencies as well as the frequency dependence of MIS capacitance and conductance at fixed gate voltages have been performed. The large frequency dispersion of MIS admittance has been observed. The model of insulator–semiconductor interface as disordered system with localized electron states distributed in energy and in space offers the possibility of an explanation of the experimentally observed broad spectrum of time constant. It has been stated that sulfur treatment of GaAs surface introduces the negative fixed charge at SiO2-GaAs interface rather than reduces the density of interface states.