K. Germanova

A vector model for analysing the surface photovoltage amplitude and phase spectra applied to complicated nanostructures

An approach is presented for comprehensive and reliable analysis of the surface photovoltage (SPV) amplitude and phase spectral behaviour in various semiconductor materials and structures. In this approach the SPV signal is represented as a radial vector with magnitude equal to the SPV amplitude and angle with respect to the x-axis equal to the SPV phase. This model is especially helpful in complicated nanostructures, where more than one SPV formation processes arises during the spectrum run. The value of the proposed model has been demonstrated by the successful explanation of seemingly contradictory SPV amplitude and phase spectra of AlAs/GaAs superlattices with embedded GaAs quantum wells, grown on different GaAs substrates. This has provided useful information about the investigated nanostructures. The need for simultaneous examination of both SPV amplitude and SPV phase spectra in order to obtain a correct understanding of the experimental data is emphasized.

An improved apparatus for surface photovoltage studies with a bimorphous piezoelectric Kelvin probe

An improved apparatus for measuring surface photovoltage spectra of semiconductors is described in which a boss-shaped Kelvin reference electrode is oscillated by using a bimorphic piezoelectric driver. A sensitivity of 0.1 mV is achieved. The apparatus is small in size, easy to handle and is compatible with the VSK 4-300 Leybold Heraeus optical cryostat allowing the range from liquid helium to room temperature to be covered.

Nonexponential deep level transient spectroscopy analysis of moderately doped bulk n‐GaAs

A theoretical analysis is carried out of deep level transient spectra (DLTS) obtained on bulk moderately doped n‐GaAs. The semiconductor is considered as a disordered one because fluctuations in the concentration of shallow donors and acceptors produce a random potential energy with a root‐mean‐square (RMS) fluctuation comparable to the mean thermal energy of the electrons. As a result, the energies of the deep levels obey a Gaussian distribution of the same RMS deviation. An original algorithm for the computer simulation of DLTS spectra is presented. The corrections to the peak energy and concentration of deep levels due to the random potential are estimated. Useful theoretical information about the microscopic parameters of the disordered system is presented as well. The degree of compensation of the material is determined.

Characterization of interface electrical properties in SiO2/InSb metal/insulator/semiconductor structures prepared by plasma-enhanced chemical vapour deposition

Abstract The preparation of dielectric layers possessing good insulating and interface properties is most important for metal/insulator/semiconductor applications. This problem presents a considerable challenge in the case of narrow gap semiconductors. In this paper we report on the electrical properties of metal/insulator/ semiconductor structures produced on p-InSb(111) by plasma-enhanced chemical vapour deposition of SiO 2 . The interface electrical properties are characterized by low and high frequency capacitance-voltage techniques in the temperature range 4.2–77 K. An appropriate theoretical model is employed for evaluation of the experimental data in which the non-parabolicity of the InSb conduction band, the incomplete ionization and recharging of dopants and the degenerate statistics are taken into account. The applicability of plasma-enhanced chemical vapour deposition for metal/insulator/semiconductor device preparation on InSb is demonstrated.

Investigation of the system InSbSiO2 by spectroscopic multiangle ellipsometry

Abstract We have characterized by multiangle spectroscopic ellipsometry the interface structure of silicon oxide plasma deposited on 〈111〉 p-type InSb substrates. Measurements have been performed with a step of 10 nm in the 400–800 nm spectral range for different angles of incidence between 40° and 80° with a 5° step. This large set of experimental data is used for solving the inverse ellipsometric problem with different structure models. Minimization procedures and merit function have been discussed. The layered structure from the best-fit model fits well the elemental distribution obtained from Auger analysis. The comparison of the dispersion of the optical constants of bulk InSb obtained on the basis of this model with the available literature data also reveals good agreement.

Optical properties of multi-layer type II InP/GaAs quantum dots studied by surface photovoltage spectroscopy

We present a low-temperature (73 K) study of the optical properties of multi-layer type II InP/GaAs self-assembled quantum dots by means of surface photovoltage (SPV) spectroscopy, taking advantage of its high sensitivity and contactless nature. The samples contain 10 periods of InP quantum dot planes separated by 5 nm GaAs spacers. The SPV amplitude spectra reveal two major broad peaks, situated at low and high energies, respectively. These features are analyzed taking into account the type II character of the structure, the quantum coupling effects, the spectral behavior of the SPV phase, and the photoluminescence spectra. As a result they have been attributed to optical transitions in the quantum dots and the wetting layers, respectively. The main mechanism for carrier separation in the SPV generation process is clarified via the analysis of the SPV phase spectra. The influence of the substrate absorption on the SPV spectra is discussed in details.

EL2 deep level in sub-bandgap surface photovoltage spectra in GaAs bulk crystals

Experimentally observed surface-photovoltage-method (SPV) spectra in the subbandgap energy range are presented for a real (100)GaAs surface, treated with preepitaxial procedures. Conductive, n-type GaAs and semi-insulating GaAs are studied. It is shown that SPV spectra are formed as a result of the simultaneous action of both surface states and deep bulk levels. The spectral shape of the surface-state photoionization cross-section is qualitatively determined. The influence of the deep bulk levels on the SPV spectra is explained, and the photoionization cross-section for both Cr and EL2 levels is qualitatively determined.

A surface photovoltage spectroscopy study of GaAs/AlAs complicated nanostructures with graded interfaces

We present a surface photovoltage (SPV) spectroscopy study of the optical properties and the bound states of graded interface AlAs∕GaAs superlattices (SLs) containing two GaAs embedded quantum wells (EQWs) with different widths. SPV spectra are measured in the metal-insulator-semiconductor operation mode under super-band-gap optical excitation at room temperature. In spite of the relatively large absorption of the GaAs substrate, the SPV spectra exhibit clearly resolved features superimposed on the substrate smooth background. These features have been identified as free exciton transitions in the EQWs and in the SL. This interpretation is based on a detailed comparison of the SPV results with those of electronic structure calculations and photoluminescence spectral measurements. The calculations are performed in frames of the envelope function approximation, employing a model structure very similar to the real one and taking into account the interface grading. The mechanisms of the SPV signal generation h...

Surface quantization effect on the macroscopic characteristics of semiconductor space-charge layers

Abstract A numerical study of the dependence of the space-charge density Q sc on the surface potential Ψ s in a two-dimensional electron inversion layer on Si(100) is presented. The dependence Q sc (Ψ) s being a macroscopic characteristic of semiconductor space-charge layers is found to be considerably influenced by the surface quantization in a wide temperature range up to room temperature. The conditions for the appearance of appreciable differences in the behaviour of the Q sc (Ψ) s curves in the quantum-mechanical and quasi-classical cases are determined and discussed.

Highly sensitive automated setup for measuring surface photovoltage spectra

We present an automated experimental setup for dc measurement of surface photovoltage (SPV) spectra in wide spectral and/or temperature ranges. A Pt boss, sealed on a bimorphic piezoelement, has been used as a small area vibrating electrode and a programmable digital‐to‐analog convertor (DAC) as a source of compensation. In addition, a combination of automatic data acquisition and statistical analysis has been applied, thus ensuring reliability and stability of SPV measurements. Moreover, the automated setup provides a high sensitivity and objectivity of SPV investigations.