Ch. Hardalov

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.

Behavior of an EL5-like defect in metalorganic vapor-phase epitaxial GaAs:Sb

An EL5‐like trap in metalorganic vapor‐phase epitaxially grown GaAs:Sb has been detected by deep‐level transient spectroscopy. The trap behavior has been investigated by changing the growth conditions—the V/III ratio and the level of isoelectronic doping with Sb. It has been found that the activation energy of the EL5‐like trap changes from Ec−0.43 eV in the undoped GaAs to Ec−0.35 eV in highly Sb‐doped GaAs. It has been observed that the EL5 trap concentration increases with increasing the [AsH3] partial pressure in the undoped material, whereas it decreases with Sb doping in correlation with EL2 kinetic decrease. The results obtained suggest that the complex defect VGaAsi can be a possible candidate for the origin of the EL5‐like trap.

Inverse problem for the nonexponential deep level transient spectroscopy analysis in semiconductor materials with strong disorder: Theoretical and computational aspects

A new method for nonexponential deep level transient spectroscopy (DLTS) theoretical analysis is proposed. This method is based on the numerical solving of the inverse problem for the theoretical model via regularization algorithms. It is shown that it is possible to obtain the shape of the deep level energy spectrum from the noisy DLTS spectra in systems with strong disorder.A new method for nonexponential deep level transient spectroscopy (DLTS) theoretical analysis is proposed. This method is based on the numerical solving of the inverse problem for the theoretical model via regularization algorithms. It is shown that it is possible to obtain the shape of the deep level energy spectrum from the noisy DLTS spectra in systems with strong disorder.

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.

Investigation of radiation damage in silicon produced by fast neutron irradiation with lifetime measurements and deep level transient spectroscopy

Deep level transient spectroscopy (DLTS) and lifetime measurements were carried out on silicon p + nn + diodes before and after irradiation with fast neutrons at room temperature with fluences of 5.5 x 10 11 and 1.0 x 10 12 n/cm 2 . In the non-irradiated samples the observed levels satisfactorily explained the measured data of recombination and generation lifetimes in the frame of the Shock-ley-Hall-Read (SHR) theory. After irradiation the lifetime data showed discrepancies with the parameters of the existing levels, which was explained by the cluster structure of the neutron damage defects.

On the applicability of deep-level transient spectroscopy for the investigation of deep centers in silicon created by fast neutron irradiation

Deep-Level Transient Spectroscopy (DLTS) measurements were carried out on silicon p+nn+ diodes before and after irradiation with fast neutrons at room temperature with fluences 5.5×1011 and 1.0×1012 n/cm2. It was found out, that all preexisting defects decreased their amplitudes during irradiation, while only one defect, identified as a single-charged divacancy, increased in amplitude. An interpretation is proposed in terms of the cluster model, and the applicability of the DLTS is 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.

Surface space-charge layer analysis in semi-insulating GaAs containing deep levels in bulk

A computer simulation study of space-charge layers at the surface of semiinsulating GaAs containing deep EL2 and Cr centers in bulk is presented. Substantial influence of the deep bulk levels on the main characteristics of the surface space charge layers, is demonstrated. The special features of these characteristics and the conditions of their arising are discussed.

On the maximum in Hall coefficient temperature dependence in medium-doped n-GaAs

Hall coefficient and conductivity are measured in a wide temperature interval from 14.5 to 295 K in order to characterize n-type GaAs bulk monocrystals with moderate donor concentration 1017–1018 cm−3. The weak temperature dependence of the Hall coefficient, showing a slight maximum at 120 K, is analyzed for the first time in terms of the model developed by Klotynsh and Bariss of discrete local levels degenerate with the continuum. For that purpose the presence of a discrete donor level degenerate with the conduction band is supposed and its energy position is calculated using the model. The concentration and the degeneracy factor of this level are determined by fitting the theoretical temperature dependence of the free electron concentration to the experimental one, the former being calculated using the charge neutrality equation. In addition, a qualitative interpretation of the Hall mobility temperature dependence is given.