O.Yu. Borkovskaya

Morphology and interfacial properties of microrelief metal–semiconductor interface

Abstract The effect of the morphology of Au/GaAs interface microrelief, prepared by chemical anisotropic etching, on current flow mechanism, electronic and recombination properties of interface has been investigated. Simulation of I – V curves and optical transmittance of light into semiconductor was made on the basis of the developed theories taking into account the barrier height distribution and the effect of scattering of light by low microrelief.

Texturized interface as a basis of surface-barrier heterostructure for solar cells application

Simulation of the photocurrent of surface-barrier structures (SBS) with texturized interface has been performed on the basis of obtained theoretical expression for internal quantum efficiency of homogeneous SBS and the model of parallelly connected diodes. The role of various sources of recombination losses (in the semiconductor, at the interface and due to the emission of majority carriers into the metal) in solar energy convertors has been analyzed. The complex method of characterization of SBS with texturized interface is proposed that includes an analysis of optical, electric and photoelectric characteristics. The possibility to increase the photosensitivity of the Au/GaAs SBS due to texturization and sulfur passivation of the interface for two types of microrelief (dendritic and quasigrating) obtained by wet anisotropic etching has been investigated. The morphology and statistical geometric characteristics of the interface were investigated by atomic force microscopy (AFM). The obtained results allowed to determine the change of optical and electronic (recombination) parameters of the interface caused by the used processing (texturization, passivation).

Analysis of thin film surface barrier solar cells with a microrelief interface

The influence of a microrelief interface between a thin conductive film (emitter) and a semiconductor substrate (absorber) on the optical and recombination losses in surface barrier solar cells is analyzed. Equations for the calculation of monochromatic light transmission through a thin absorbing film with one or two rough surfaces, on an absorbing substrate, are presented. For a weakly texturized interface and a normal direction of the incident light, the influence of the microroughness is taken into account by the formulae obtained. A model of patches with microsurfaces parallel to the structure surface and ones inclined to it at a certain angle (the most probable statistically) was used to describe the experimental results. Au/GaAs surface barrier structures with interface microrelief of a quasigrating or a dendritic type, obtained by chemical anisotropic etching of GaAs, were investigated. The geometric and statistical parameters of the microrelief were determined by atomic force microscopy techniques. The recombination parameters of the textured interfaces were determined from the experimental spectra of the external quantum efficiency, taking into consideration the calculated spectra of light transmittance. A comparison of the internal quantum efficiency spectra with the calculated ones allows a determination of the electronic parameters of the interface. Both the photoconversion parameters under AM0 simulated illumination and the tolerance for 60Co γ-irradiation, obtained for structures with various interface microrelief morphologies, allowed identification of microrelief of the quasigrating type as more suitable for solar cell applications.

Polarization-sensitive photocurrents of metal-semiconductor structures with flat and microrelief interfaces

Abstract The dependence of the polarization photosensitivity on parameters of a multilayer surface-barrier structure (SBS) (metal (Ag, Au) - intrinsic oxide - isotropic semiconductor (InP, GaAs)) with flat and microrelief interfaces has been studied. The influence of metal layer thickness on the polarimetric effect was analyzed. Both spectral and angular characteristics of the SBS polarization photosensitivity were calculated. Comparisons between the calculated angular characteristics of transmission coefficients for the light and those of the measured short-circuit photocurrent i ph for several wavelengths were made. To account for a micro-relief effect on the SBS polarization photosensitivity, the equivalent film method was used. The surface polariton excitation was shown to be an additional mechanism of photosensitivity enhancement and affected its polarization sensitivity.

Ultraviolet responsivity control in Schottky barrier heterostructures with textured interface

This paper is devoted to ultraviolet responsivity control in Schottky barrier heterostructures based on GaAs and InP with textured interface. The influence of microrelief morphology and of its geometrical parameters on optical properties and photoresponse characteristics (spectral and polarization) has been investigated. Both random microrelief obtained by chemical anisotropic etching of semiconductor and microrelief of grating type formed by holographic etching were used. The optical and photoelectric characterization of heterostructures with textured interface allowed us to determine the most promising type of microrelief, and to define the mechanisms of the photosensitivity enhancement. Specifically, the role of surface polariton excitation as a mechanism of photoresponse increasing was treated.

Influence of modified surface of gaas on properties of heterostructures with organic semiconductors

The electrical, optical and photoelectric properties of organic/inorganic semiconductors heterostructures are investigated depending upon the interface microrelief morphology modified by chemical etching of GaAs. Polishing andanisotropic etchants were used to change it from flat to microtextured(quasigrating-type). The p/n-heterostructures were fabricated by the vacuumevaporation of thin (∼50 nm) pentacene or phthalocyanine of lead filmson modified surface of n-GaAs crystals. A considerable decrease of the optical reflectance and increase of the photosensitivity by a few (1.5-4) times have been obtained for microtextured heterostructures with respect to the flat ones.The results emphasize the importance of GaAs surface chemical microtexturing to future developments of the photocells, based on organic semiconductor/GaAs heterojunction.

Ultraviolet photodetector on the basis of heterojunction with textured interface

Abstract This paper is devoted to elaboration and investigation of ultraviolet photodetector (UVPD) on the basis of heterojunctions of A 3 B 5 semiconductor/transparent conducting layer with microrelief interface. The methods of random microrelief of desirable morphology fabrication for (100) GaAs and InP surfaces are described. AFM images of GaAs and InP surfaces with optimal microrelief are presented as well. The spectral responses of Au/(GaAs, InP) and ITO/GaAs photodetectors in the spectral range from 0.25 to 0.5 μm in dependence on the interface microrelief morphology and passivating treatments have been investigated. Photodetectors with enhanced UV response at λ =0.26–0.40 μm have been obtained on the basis of Au/GaAs ( S λ =0.17–0.21 A/W) and Au/InP ( S λ =0.12–0.23 A/W) heterostructures by the developed technology of interface texturation and passivation.

Effect of surface roughness on the properties of ohmic contacts to GaAs

Au/Ge/TiB/sub x//Au ohmic contacts to n-GaAs with textured surface have been developed and investigated. Two types of microrelief morphology (quasi-grating and dendrite-like), that are perspective for Solar Cell and sensor application, have been obtained by wet chemical anisotropic etching. The surface morphology and structural perfection were studied by AFM technique and x-ray diffractometry measurements. The effect of surface roughness on the value of contact resistivity and its lateral distribution has been investigated. The qualitative model for nonuniformity of ohmic contact formation caused by the dependence of intrinsic stresses on the interface roughness has been drawn to explain experimentally observed spread of electrical parameters.

Photoconverters based on gallium arsenide diffused p-n junctions formed on a microprofile GaAs surface

The p-n junctions promising for photoconverters have been fabricated using diffusion from the gaseous phase and studied with the analysis of mass transport of the doping impurity (Zn) through the microprofile GaAs surface taken into account. Depending on the conditions of diffusion (the diffusant’s mass and diffusion duration), the formation of both a p-n junction in a microprofile and a planar p-n junction in the GaAs bulk with a heavily doped near-surface p+ type layer is possible. Photoelectric characteristics of device structures with textured p-n junction and a thin wide-gap AlxGa1 − xAs window obtained by liquid-phase epitaxy are reported.

Self-organized technology of anisotropic etching of semiconductors for optoelectronics application

This paper is devoted to the investigation of self-organized microrelief morphology control for GaAs and InP substrates by varying the chemical anisotropic etching regime. The microstructure and the morphology of self-organized microrelief of quasigrating type were revealed by atomic force microscopy (AFM) technique. This type of microrelief allows in particular to obtain additional photosensitivity enhancement for Schottky barrier structures due to surface plasmon polariton excitation. The optical and photoelectric characteristics of Au/GaAs (InP) barrier structures were investigated in the range of fundamental absorption of light and the optimum microrelief processing were selected.