The signal of the Transient Microwave Detected Photoconductivity after laser pulse illumination is followed during the PECVD growth of intrinsic amorphous silicon on top of crystalline silicon (c-Si) substrates. Depending on the thickness of the amorphous layer the observed phototransients can be assigned to the excess charge carriers in different regions of the so grown heterojunction. For thin a-Si:H layers the signal amplitude decreases exponentially with deposition time. In the case of thick amorphous silicon the signal reflects only the properties of the amorphous silicon and the signal amplitude is constant. In an intermediate range a large contribution of charge carriers absorbed in the a-Si:H and subsequently transported to the crystalline part of the heterostructure to the measured signal can be observed. Due to their much higher mobility in the crystalline layer these excess charge carriers become visible only after reaching the crystalline silicon. This leads to the observed delay of the TRMC signal amplitude relative to the exciting laser pulse. The experiments show, however, that this charge carrier transfer takes place only in the case of a low defect a-Si:H layer to a measurable extent and is suppressed by the low carrier mobility in highly defective a-Si:H deposited at lower substrate temperatures.

A study of excess carrier kinetics in a-Si:H / crystalline n-Si heterojunctions by transient photoconductivity measurements as a function of the excitation density is presented. It is observed that excess carriers can be injected from the a-Si:H in the c-Si part of the junctions, where the time associated to this injection process can be clearly resolved. The number of injected carriers increases with the number of excess carriers induced in the a-Si:H at low excitation density reaching a limit in the moderate excitation range. The driving force of the injection process is tentatively ascribed to the space charge field at the interface. The injection efficiency is estimated to be about 10%.

Extension of the Kelvin probe vibrating capacitor technique of measuring work function, via Illumination of the semiconductor surface, i.e., Surface Photovoltage Spectroscopy (SPS), has many potential applications in the field of surface analysis.

The combination of broad-band (white) and monochromatic radiation, together with measurement of the dark signal permits complete characterisation of the semiconductor work function via determination of the electron-affinity, surface potential and Local DensIty-of-States (LDOS). The work function is an extremely sensitive indicator of a wide range of surface processes, e.g., particle adsorption, stress, defect creation, phase-transitions, etc.

We Illustrate application of this technique in the study of the temperature dependent initial oxidation behaviour of p-type Si(111) 7×7 between 100 and 300 K. The SPV response of the clean surface at 100 K corresponds to the capture of photo-stimulated electrons by a band of surface states centered around 1.4, 1.7, 1.9 and 2.4 eV. This response completely disappears at the peak of the (dark) work function change (0.3L) corresponding to a near complete removal of dangling bond states. The temperature-dependent white-light SPS response permits determination of the band-bending throughout the adsorption process. We observe that at 100 K the band-bending substantially decreases during the initial adsorption phase (0.1 L), after this dose it remains constant. However at 300 K the band-bending decreases much later, i.e., >10 L, in conjunction with oxygen permeation through the surface layer.

In conclusion Surface Photovoltage Spectroscopy SPS is a simple and flexible method which can be used to follow the rather complex changes occurring at the semiconductor surface. It is a non-contact, nondestructive technique which allows simultaneous determination of both semiconductor band-bending and electron affinity.

A novel technique for characterizing the variation of depletion width versus reverse bias voltage, the absorption coefficient, and the defect density in amorphous silicon thin films has been developed. The technique utilizes the fact that the rate of change of dc photocurrent with reverse voltage in a photodiode is strongly dependent upon the wavelength of light.

A set of experimental measurements concerning both current noise and conductance relaxation curves in CdS and CdSe photoconductors has shown the existence of a relationship between the noise power spectrum and the Fourier transform of the phototransient curve. Some of these experimental results have already been published. It appears that at least two different noise components contribute to the total power spectrum. The first component, which dominates the low frequency part of tile spectrum, is strictly related to the behaviour of the relaxation curve. Indeed, it can be attributed to the fluctuation of the photoinduced positive trapped charge and consequently of the potential barrier at the interface electrode-photoconductive material. The second component, on the contrary, is practically independent of the light wavelength, and represents an intrinsic noise component related to the generation-recombination and trapping processes within the photoconductor. In this paper we present a theory accounting for both the photoinduced and the intrinsic noise component. This theory fits well to the experimental data concerning the dependence of noise on light intensity and wavelength, using the parameters obtained from the phototransient and photoconductance measurements performed on thle same specimens. It also gives tile correct order of magnitude of the measured absolute value of the noise power spectrum.

The present work confirms thee possibility of chaotic behavior in intrinsic photoconductors with one type of traps under high radiation intensity. The system shows two attractors and a strong sensitivity to the initial conditions.

Germanium Blocked Impurity-Band (BIB) detectors, which have potential applications for space-born far infrared astrophysics observations, have been fabricated by means of boron ion implantation on high-purity Ge substrates. These devices are sensitive beyond the cutoff wavelength of Ge photoconductors doped with shallow acceptors. The extended cutoff wavelength increases with applied bias and can reach up to 200μm at very low dark currents of less than 100 electrons/sec. In order to enhance the photo-response, high-energy (3MeV) implantation has been used to form a thicker infrared-active layer. The influence of both ion-implant energies and post-implant anneals on the performance of detectors will be presented. Generation of excess donors in the boron implanted region has been observed. Their origin and effect of device performance will be discussed.

Dynamic gratings of free carriers are generated from optical excitation of the deep EL2 level in semi insulating gallium arsenide with nanosecond pulses. The nonlinear modification of the crystal index of refraction is evidenced by degenerate four wave mixing experiments. In regards to the sample parameters, a fair agreement is obtained between the experimental values and the theoretical predictions derived from the Drude-Lorentz model and the anharmonic motion of carriers.

We studied the pump intensity dependence of the 2WM gain in a photorefractive GaAs:EL2 crystal, with a 3.3 kV/cm d.c. field, at two different wavelengths. The grating period was 37 Am and the beam ratio was 4. At 1.32 μm, the characteristics exhibits a resonant behaviour (with a maximum of 0.23 cm-1). As for InP:Fe, these results can be explained by considering that thermally and optically generated carriers are of different types. The curve at 1.047 Am exhibits an original feature. At low intensities the gain as the same sign than at 1.32 μm (with a maximum of 0.12 cm-1), but the sign changes with increasing intensity and the gain tends towards an asymptotic value of -0.15 cm-1. Such behaviour may also be explained with the same model.

A finite difference technique was used to model photorefractive grating formations under conditions of moving gratings and large modulation. These results were generalized through analytical expressions which approximate the numerical solutions.

High-order spatial harmonics of photo-induced space-charge gratings are observed in semi-insulating photorefractive quantum wells. Two-wave mixing combined with four-wave mixing in holographic thin films can provide a versatile probe of absorption and photorefractive gratings.

We propose a multilayer photorefractive device based on the association of two classes of materials respectively designed for transport and electro-optic properties. This device consists in repeated elementary cells, each of them made with an electro-optic material layer embedded between two different photoconductive layers. In these layers (respectively hole and electron dominated) deep levels allow to build-in a space charge field distribution under periodic illumination, giving rise in the electro-optic layer to a perpendicular electric field component, yielding to a diffraction grating. Its efficiency can be increased by the repetition of these cells. InGaAsP/InP MQW can be used as electro-optic material and semi-insulating InP:Ti and InP:Fe as respectively electrons and holes dominated photoconductors. We present simulation results of the behaviour of this device under electric bias and of the coupling effects between adjacent layers which yield space charge field modulation well over the usual diffusion limit.

This work reports on the theoretical modeling and experimental investigation of isothermal SPV-DLTS based on the rate window concept. Experimental implementation of the technique is done using computer analysis of the SPV transients after ceasing the illumination. The transient involves two processes – a recombination of excess minority carriers and a thermal emission of carriers trapped by surface states and bulk defects. The later process is the key one for deep level defect determination.

The upper limit for the measurable deep level emission rate is provided by the recombination lifetime. This limit often exceeds, by orders of magnitude, the standard 103 s−1 limit in capacitance DLTS. The sensitivity of SPV-DLTS is of the same order as that of optical capacitance DLTS.

We present fast, wafer-scale imaging of the surface charge achieved via non-contact measurement of the surface potential barrier by surface photovoltage (SPV) under high excitation levels. The approach is capable of resolving surface charge differences as small as 108 q/cm2. Fundamentals of surface charge imaging are discussed, and the method is compared with standard SPV contamination mapping. Examples include problems relevant to silicon IC fabrication and surface charge maps of GaAs and InP.

A complete understanding of the electrical and optical properties of the Vanadium related donor level (VGa3+/VGa4+) in GaP is deduced from a number of different characterization techniques (deep level transient and deep level optical spectroscopies, optical absorption) performed on p-type V doped GaP. The VGa3+/VGa4+ donor level is located at Ev+0.25eV. This assignment is based on the correlation of optical absorption spectra and the photoneutralization cross-section σp°(hv) curve obtained by deep level optical spectroscopy confirming that this technique is very unique for deep level identification in semiconductor materials.

A noncontact technique for deep level energy analysis has been discussed based on a laser excitation/microwave reflection transient photoconductance procedure. An algorithm for separation of surface and bulk recombination effects was developed to independently determinesurface and bulk energy states. Deep energy levels associated with trapping and recombination processes have been calculated from the temperature dependence of surface recombination velocity and bulk recombination lifetime, based on state occupation statistics. Results have been compared with conventional DLTS data for silicon samples intentionally doped with metals during crystal growth.

A high resolution spatially resolved photocurrent system to study bulk non homogeneities in semiinsulating GaAs and InP is described. [Fe+3] distribution is studied in InP. In undoped LEC semiinsulating GaAs a study of the relation of Photoquenching (PQ) and Enhanced Photocurrent (EPC) to the dislocation atmosphere is done.

Influence of processing conditions on electrophysical properties of composite materials (CM) have been investigated. Metal powders, graphite, Z-ferrite and other fillers were used. Properties of CM were investigated in direct and alternating electromagnetic fields.

By correlating the results of photoreflectance, photoconductivity, photoluminescence, and differential-Hall and photo-Hall measurements with the stoichiometry, for a number of undoped single crystal samples, we could conclude two donor levels (35 meV, 70 meV) and three acceptor levels (100 meV, 155 meV, 170 meV) distributed in the forbidden ga.p for undoped CuInS2 samples.

The electron and hole traps in semi-insulating (SI) GaAs can not be identified by common Photoinduced Current Transient Spectroscopy (PITS) and Thermally Stimulated Current (TSC) measurements because of appearing of same sign signal for electrons and holes in both experiments. Therefore, we have developed two approaches which could be used to identify the type of the traps, and the origin of the puzzling negative peaks in the PITS spectra.

The TSC and qusi-stationary Hall effect measurements have been simultaneously performed at the temperatures between 77K and 300K. The sign of Hall voltage corresponding to TSC peak shows the type of the trap.

PITS spectra with applying different bias polarity to the sample were carefully measured with below gap and above gap photoexcitation. According to the change of PITS peak's height with different bias polarity, the electron and hole traps could be readily distinguished, since a negative bias makes hole no contribution to the PITS signal whereas electron swept into the sample would fill the electron traps, and consequently results in the appearence of the electron trap peaks. On the contrary, a positive bias would cause the filling of the hole traps.

The negative PITS peaks appearing or vanishing can be understood if one takes into account the trap initial filling conditions, the carrier recapture and the high dark current etc.