Porous GaAs Substrates Research Articles

The temperature dependence on the electrical properties of dysprosium oxide deposited on n-porous GaAs

This paper describes the electrical and dielectric characteristics for the first time of the high-k Dy2O3 oxide film deposited on the porous GaAs substrate by electron beam deposition under ultra vacuum. Morphological characterization is investigated by atomic force microscopy (AFM). The electrical and dielectric properties of Co/Au/Dy2O3/n-porous GaAs structure were studied in the temperature range of 80–500 K. The conductance and capacitance measurements were performed as a function of bias voltage and frequency. The dielectric constant (ε′), dielectric loss (ε″) and dielectric loss tangent (tanδ) of the structure are obtained from capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. These parameters are found to be strong functions of temperature and bias voltage. In the forward bias region, C–V plots show a negative capacitance (NC) behavior, ε′–V plots for each temperature value take negative values as well. Such negative values of C correspond to the maximum of the conductance (G/ω). The negative capacitance values appear abnormal when compared to the conventional behavior of ideal Schottky barrier diode (SBD) and metal–oxide–semiconductor (MOS) structures. The following behavior of the C and ε′ in the forward bias region has been explained with the minority-carrier injection and relaxation theory. From DC conductance study, electronic conduction is found to be dominated by thermally activated hopping at high temperature. Activation energy is deduced from the variation of conductance with temperature. The Nyquist plots exhibited single semi-circular arcs which were well fitted to an equivalent circuit.

Comparative study of structural and visible luminescence properties of AZO thin film deposited on GaAs and porous GaAs substrates

The objective of this study is to investigate the effect of the pre-treatment of GaAs substrate by making it porous on structural and visible luminescence properties of aluminum - doped zinc oxide (AZO) thin films deposited by the use of a radio frequency magnetron sputtering. Porous GaAs has been prepared by anodic etching of n+-type (100) GaAs wafers in a HF:C2H5OH:HCl:H2O2:H2O electrolyte. Structural and visible luminescence properties of deposited films have been investigated by means of x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and room temperature photoluminescence (PL) spectroscopy. XRD patterns of deposited films show predominant orientation along (100) crystal plane of hexagonal ZnO. A diffraction peak due to cubic zinc arsenide (Zn3As2) is only observed in the XRD pattern of the film deposited on porous GaAs. XPS results further confirm that the AZO film deposited on porous GaAs is doped with arsenic (As). This is attributed to the enhancement of As diffusion into the film due to nanostructure nature of porous GaAs. The use of porous GaAs as a substrate also leads to an enhancement of the visible PL intensity of the deposited film. This is found to have a strong relationship with the change in the content of zinc and oxygen related defects in the film as it is revealed from peak analysis of XPS and PL spectra.

Misfit dislocation reduction in InGaAs epilayers grown on porous GaAs substrates

Abstract Elastic accommodation of heteroepitaxial layers beyond their critical thickness is crucial for the reduction of misfit dislocations. One approach is to utilize substrate engineering in order to delay plastic relaxation. In this work, pore networks were introduced electrochemically in GaAs substrates in order to modify their mechanical responses. In x Ga 1− x As epilayers with nominal indium contents up to x = 0.20 were then deposited by MOVPE, and were compared to similar epilayers grown on nonporous GaAs. Strain relaxation and defect introduction were studied by TEM observations, x-ray diffraction, and photoluminescence measurements. It was found that the porous substrates acted to reduce the density of misfit dislocations, thereby increasing the epilayer critical thickness. The InGaAs epilayers retained a significantly higher amount of elastic strain compared to ones grown on nonporous GaAs. The onset of plasticity was mediated by the pores, which acted as nucleation sites for 60° dislocations that glided toward the interface.

Epitaxial growth on porous GaAs substrates

Abstract We report on the electrochemical preparation of porous GaAs substrates in fluoride-iodide aqueous electrolytes for the lattice mismatched epitaxial growth from the vapor phase. The aim is to gain control over the uniformity of the pore nucleation layer and pore branching below this layer to achieve structures with a high degree of porosity and periodicity while leaving minimum damage on the substrate surface. Layers of InxGa1-xAs with varying In content are grown on GaAs substrates with different pore geometries and depths. Substantial differences in the surface morphology and photoluminescence efficiency of the layers grown on porous and conventional substrates are observed.

Preparation of nanoporous GaAs substrates for epitaxial growth

AbstractWe report on the electrochemical preparation of porous GaAs substrates suited for the lattice mismatched epitaxial growth from the liquid and vapour phase The aim is to gain control over the uniformity of the pore nucleation layer and pore branching below this layer to achieve structures with a high degree of porosity and periodicity. The etching process should be surface‐friendly and leave minimum damage on the substrate surface to be ready for the subsequent epitaxial growth. We show that surfaces with different pore diameter, pore spacing and surface roughness can be achieved by careful selection of the etching regime, electrolyte, and substrate. Moreover, the pore depth, pore density and pore branching can be tailored to comply with the subsequent epitaxial growth (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal conversion and epitaxial overgrowth of nanopores etched in InP and GaAs

Both crystallographically oriented and current line oriented pore networks in InP and GaAs are created by electrochemical dissolution. Heat treatment of InP pores at 650°C and of GaAs pores at 700–850°C converts them into microcavities maintaining almost the same crystallographic direction. As a transition between micro/nanopores and micro cavities the lamellar structures are obtained. Mass transport is responsible for the pore conversion. The effect of 'anion' vapour pressure is proved to be crucial for the microcavity formation since it influences the mass transport during the heat treatment. Electron microscopy and photoluminescence experiments reveal the absence of significant extended defects, both after the formation of pores and cavities. The capability of improved structural quality of homo– and hetero–epitaxially overgrown films on porous InP is demonstrated by liquid phase epitaxy growth of InP and InAs. Overgrowth of the porous GaAs substrates by ternary GaInAs layers with different lattice mismatch was realised by metal organic vapour phase epitaxy.

PROPERTIES OF GaNAs AND GaN, OBTAINED BY NITRIDATION OF POROUS GaAs SUBSTRATE

Result of photoluminescence investigation of thin films of GaNAs compound, obtained by nitridation of porous GaAs substrate are presented in the article. It has been found possible to control of arsenic and nitrogen concentration in GaNAs by optimizing the condition of annealing in atomic nitrogen. Cubic GaN film were obtained on por-GaAs/GaAs(111) substrate, that extends possibility of growth GaN cubic on GaAs substrate. Effect of changing of the energy of the band-edge luminescence of GaNAs from 2.63 to 2.44 eV with increasing arsenic concentration from 1 to 10% are discussed. The dependences of lattice type of GaN films on porosity of por-GaAs/GaAS(111) are reveals. It has been determined, that using porous GaAs substrate with porosity of 30% favours formation of cubic GaN. Photoluminescence peak at 3.42 eV (at 77 K) is attributed to polycrystalline hexagonal inclusion in cubic GaN.

Morphology and optical properties of p-type porous GaAs(1 0 0) layers made by electrochemical etching

Porous GaAs layers were formed by electrochemical etching of p-type GaAs(1 0 0) substrates in HF solution. A surface characterization has been performed on p-type GaAs samples using X-ray photoelectron spectroscopy (XPS) technique in order to get information about the chemical composition, particularly on the surface contamination. According to the XPS spectra, the oxide layer on as-received porous GaAs substrates contains As 2O 3, As 2O 5 and Ga 2O 3. Large amount of oxygen is present at the surface before the surface cleaning. Compared to untreated GaAs surface, room temperature photoluminescence (PL) investigations of the porous layers reveal the presence of two PL bands: a PL peak at ∼871 nm and a “visible” PL peak at ∼650–680 nm. Both peak wavelengths and intensities varied from sample to sample depending on the treatment that the samples have undergone. The short PL wavelength at 650–680 nm of the porous layers is attributed to quantum confinement effects in GaAs nano-crystallites. The surface morphology of porous GaAs has been studied using atomic force microscopy (AFM). Nano-sized crystallites were observed on the porous GaAs surface. An estimation of the mean size of the GaAs nano-crystals obtained from effective mass theory and based on PL data was close to the lowest value obtained from the AFM results.

Structural characterisation of CdS layers deposited on porous p-type GaAs

The purpose of this paper is to investigate the initial stage of cadmium sulphide (CdS) layer deposited on porous p-type GaAs substrate by vacuum evaporation technique. The deposited CdS layer was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). SEM imaging shows that the CdS was penetrated deeply in the porous structure down to the bottom and reaching the interface GaAs/porous GaAs. The AFM image demonstrates that the CdS deposited are grains of several nanometres and XRD patterns exhibit that the deposited layer has a hexagonal prominent phase.

Growth and defects of GaAs and InGaAs films on porous GaAs substrates

We investigated the opportunities to increase the electric uniformity of GaAs and InGaAs films grown by molecular-beam epitaxy (MBE) technique on monocrystalline (single crystal) GaAs: both on porous and conventional so-called “monolithic” (without pores) GaAs (100) substrates. The basic attention was given to study the electrically active defects in films by using scanning electron microscope (SEM) with new technique which is called “Rau-detector” [E.I. Rau, A.N. Zhukov and E.B. Yakimov, Solid-State Phenomena, 1998, v. 53–54, 327.]. We compared the main properties of epitaxial GaAs and InGaAs films grown on above mentioned substrates. The films grown on porous substrates had higher structural perfection including the following advantages: ( a) smoother surface due to lateral growth mechanism; ( b) less density of structural defects (without dislocation walls), the density of pyramidal defects was ∼ 2 × 10 5 cm − 2 as compared with the density 2 × 10 7 cm − 2 in the films grown on monolithic substrates; ( c) less electrical activity of various structural defects and increased electric uniformity of grown films. The electrical activity of defects in films grown on porous substrates was essentially lowered due to gettering properties of porous substrate.

Strain Relaxation in Zincblend GaN Layers on Porous GaAs (001) Substrates

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Properties of cubic GaN films obtained by nitridation of porous GaAs(001)

AbstractWith the help of nitridation of porous GaAs(001) in nitrogen plasma thin films of cubic‐GaN were obtained. The conclusion was made that the quality of the GaN films is dependent on the degree of porosity of the GaAs substrate. XPS spectra were used to investigate the chemical composition of porous GaAs substrates, obtained by electrochemical etching. Porous GaAs substrate at first was annealed in a H2 flow at a temperature of 550 °C (with the aim of removing oxygen from the surface of the porous GaAs). Then, the porous GaAs substrate was annealed in atomic nitrogen at a temperature of 400 °C, and then annealed in vacuum at 600 °C. From XPS measurement we determined that the annealing in atomic nitrogen leads to the formation of GaN films. X‐ray diffraction measurements show that cubic GaN on porous GaAs substrate has no tensile strain. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Long-wavelength emission from single InAs quantum dots layer grown on porous GaAs substrate

In this paper, we present the growth and photoluminescence (PL) results of InAs quantum dots (QDs) on a p-type porous GaAs (001) substrate. It has been shown that critical layer thickness of InAs overgrowth on porous GaAs has been enhanced compared to that deposited on nominal GaAs. Using porous GaAs substrate, growth interruption and depositing 10 atomic monolayer (ML) In0.4Ga0.6As on InAs QDs, photoluminescence measured at 10K exhibits an emission at 0.739eV (∼1.67μm) with an ultranarrow full width at half maximum (FWHM) of 16meV. This emission represents the longer wavelength obtained up to date to our knowledge and has been attributed to the radiative transition in the InAs QDs.

Ultraviolet luminescence of thin GaN films grown by radical-beam gettering epitaxy on porous GaAs(111) substrates

GaN films with a thickness of 0.1 µm were grown by radical-beam gettering epitaxy on porous GaAs(111) substrates. Excitonic luminescence bands are dominant in the photoluminescence spectra measured at 4.2 K. The energy positions of excitonic-band peaks are analyzed; as a result, it is concluded that there are stresses in the grown GaN films.

Critical layer thickness enhancement of InAs overgrowth on porous GaAs

In the present work we have investigated the initial stage of InAs layer grown on porous GaAs (π-GaAs) substrate by using reflection high-energy electron diffraction (RHEED) and low temperature photoluminescence (PL). RHEED measurements show that the 2D–3D growth mode transition appears after a deposition of 4.2 atomic monolayer (ML) of InAs, which is higher than that deposited on nominal GaAs (1.7 ML). PL investigations show two luminescence bands at 1.24 and 1.38 eV. The 1.24 eV PL peak emission is associated to the radiative transitions in InAs quantum dots (QDs), whereas the 1.38 eV PL peak emission is attributed to the InAs wetting layer (WL). The results show that π-GaAs is a promising candidate to obtain a reduced QDs size distribution, and to grow pseudomorphic epitaxial layer on GaAs substrate with higher indium concentration.

Photoluminescent and structural properties of GaN thin films obtained by radical-beam gettering epitaxy on porous GaAs (0 0 1)

Cubic GaN (c-GaN) layers were grown on porous GaAs (001) substrate by radical-beam gettring epitaxy. X-ray difraction and photoluminescence measurement indicate that the both single crystalline cubic GaN and hexagonal GaN was successfully grown on the porous GaAs (001) substrate.

Single-crystalline GaAs, AlGaAs, and InGaAs layers grown by metalorganic VPE on porous GaAs substrates

Conditions for the growth of single-crystalline GaAs, AlGaAs, and InGaAs layers by metalorganic VPE were established and the corresponding semiconductor films were obtained on porous GaAs substrates. Comparative data on the morphology, structure, and electrical homogeneity of the epitaxial layers grown on the porous and monolithic substrates are presented. It was found that passage to the porous substrates leads to changes in the film growth rate and morphology, the concentration of electrically active defects, and their distribution in depth of the epitaxial structures.

Unstrained epitaxial InxGa1−x As films obtained on porous GaAs

Epitaxial layers of InGaAs solid solutions were grown on porous GaAs(100) substrates by liquid-phase epitaxy. A comparison between the compositions and thicknesses of these epitaxial layers with those of layers obtained under the same conditions on normal monolithic GaAs substrates suggests that the crystallization of epitaxial layers on porous substrates may be considered as the growth of free unstrained films.

Growth of cubic GaN by molecular-beam epitaxy on porous GaAs substrates

It is shown that GaN layers can be grown on (100)-and (111)-oriented porous single-crystal GaAs substrates by molecular-beam epitaxy with plasma activation of the nitrogen by an rf electron cyclotron resonance discharge. The resulting undoped epitaxial layers possessed ntype conductivity with a carrier concentration ∼1018. Data obtained by scanning electron microscopy and cathodoluminescence indicate that at thicknesses ∼2000 A, continuous layers of the cubic GaN modification are obtained regardless of the substrate orientation.