A. Uleckas

Instrumentation for the in situ control of carrier recombination characteristics during irradiation by protons

Instrument and methods for the remote and in situ control of carrier recombination parameters during irradiation by protons of energy in the range of 3-8 MeV are presented. Direct techniques for measurements and separation of carrier recombination and trapping/generation characteristics based on the analysis of microwave probed photoconductivity transients during exposure on protons of different energies and irradiations at different temperatures are described. Simultaneously, a spectroscopy of activation energy of dominant traps has been performed before and just after irradiation by temperature scans of variation in the recombination parameters.

Microwave probed photoconductivity spectroscopy of deep levels in Ni doped Ge

A transient technique to simultaneously measure carrier lifetime and deep levels in semiconductors is proposed based on microwave probed photoconductivity spectroscopy in the wavelength range between 0.5 and 16μm. The application of this noncontacting technique is illustrated by a study of carrier lifetime and deep levels in Ni implanted and annealed Ge wafers. The activation energies of the deep levels are determined at room temperature and compared with those extracted by means of capacitance deep level transient spectroscopy.

Barrier Evaluation by Linearly Increasing Voltage Technique Applied to Si Solar Cells and Irradiated Pin Diodes

Technique for barrier evaluation by measurements of current transients induced by linearly increasing voltage pulse based on analysis of barrier and diffusion capacitance changes is presented. The components of the barrier capacitance charging and generation/recombination currents are discussed. Different situations of the impact of deep center defects on barrier and diffusion capacitance changes are analyzed. Basics of the profiling of layered junction structures using the presented technique are discussed. Instrumentation for implementation of this technique and for investigations of the steady-state bias infra-red illumination and temperature dependent variations of the barrier capacitance charging and generation/recombination currents are described. Applications of this technique for the analysis of barrier quality in solar cells and particle detectors fabricated on silicon material are demonstrated.

Room temperature spectroscopy of deep levels in junction structures using barrier capacitance charging current transients

A technique is presented for room temperature spectroscopy of deep levels in semiconductor devices based on measurements of current transients due to barrier capacitance charging. Spectroscopic measurements are obtained from a set of the barrier capacitance charging current transients modified by illumination pulses with wavelength between 1.5 and 10 μm. Deep levels with activation energy in the range between 0.24 and 0.56 eV have been revealed in thyristor and neutron irradiated particle detector structures by using this technique.

Correlated evolution of barrier capacitance charging, generation, and drift currents and of carrier lifetime in Si structures during 25 MeV neutrons irradiation

The in situ examination of barrier capacitance charging, of generation and drift currents, and of carrier lifetime in Si structures during 25 MeV neutrons irradiation has been implemented to correlate radiation induced changes in carrier recombination, thermal release, and drift characteristics and to clarify their impact on detector performance. It has been shown that microwave probed photo-conductivity technique implemented in contact-less and distant manner can be a powerful tool for examination in wide dynamic range of carrier lifetime modified by radiation defects and for rather precise prediction of detector performance.

Analysis of Auger Recombination Characteristics in High Resistivity Si and Ge

The characteristics of the band-to-band Auger recombination in Czochralski-grown high resistivity Si and Ge single crystals have been studied using a contactless technique to measure excess carrier decay transients based on infrared absorption by free carriers. The measurements are performed using laser light excitation with wavelengths ranging from 1.2 to 2.5 µm to reduce inhomogeneity effects in the extraction of the Auger recombination parameters. A linear approximation of the initial excess carrier decay lifetime yields an approximate value of the Auger recombination coefficient in Ge γA,Ge ≈ 2×10-31 cm6/s, which is close to that in Si. These characteristics also indicate that the difference in Auger recombination coefficients for the ehh and eeh processes is small. A more detailed fitting procedure applied simultaneously on a series of experimental transients yields a more accurate value of (8±3)×10-31 cm6/s for the Auger recombination coefficient in Ge.

In situ analysis of carrier lifetime and barrier capacitance variations in silicon during 1.5 MeV protons implantation

Results of the in situ measurements of the recombination lifetime and of barrier capacitance variations in Si substrates and pin diodes, respectively, during 1.5 MeV protons implantation are presented. Carrier recombination lifetime has been measured by employing microwave probed photoconductivity method, while parameters of the barrier capacitance changes have been extracted by transient technique of barrier capacitance charging current measurements using linearly increasing voltage pulses. Sub-linear decrease of carrier lifetime as a function of fluence has been revealed and peculiarities of such characteristic are explained in terms of formation of two layered structure within implanted Si material. Carrier recombination processes determine the increase of dielectric relaxation time within electrically neutral region (ENR) of a diode base. Carrier capture/emission processes within space charge (SC) and transition layer (between ENR and SC) regions lead to increase of generation/recombination currents in the irradiated diode.

Study of deep level characteristics in the neutrons irradiated Si structures by combining pulsed and steady-state spectroscopy techniques

The standard methods, such as capacitance deep level transient spectroscopy (C-DLTS) and thermally stimulated current (TSC) techniques are unsuitable for the analysis of heavily irradiated devices. In this work, therefore, several steady-state and pulsed techniques have been combined to comprehensively evaluate parameters of radiation defects and functional characteristics of the irradiated Si pin detectors. In order to understand defects created by radiation and evaluate their evolution with fluence, C-DLTS and TSC techniques have been employed to make a baseline identification of the radiation induced traps after irradiation with a rather small neutron fluence of 1012 cm−2. The steady-state photo-ionization spectroscopy (PIS) technique has been involved to correlate thermal- and photo- activation energies for definite radiation defects. A contactless technique for simultaneous measurements of the carrier lifetime and the parameters of deep levels based on microwave probed pulsed photo-conductivity (MW-PC) spectroscopy has been applied to correlate carrier capture cross-sections and densities of the identified different radiation defects. A technique for spectroscopy of deep levels in junction structures (BELIV) based on measurements of barrier capacitance charging current transient changes due to additional spectrally resolved pulsed illumination has been applied to evaluate the functional characteristics of the irradiated diodes. Pulsed spectroscopic measurements were implemented by combining the analysis of generation current and of barrier capacitance charging transients modified by a single fs pulse of illumination generated by an optical parametric oscillator of varied wavelength in the range from 0.5 to 10 μm. Several deep levels with activation energy in the range of 0.18–0.8 eV have been resolved from spectral analysis in the samples of Si grown by magnetic field applied Czochralski (MCz) technology.