Jick H. Yee

What Can Be Expected from High-Z Semiconductor Detectors?

It has been hoped that high-Z semiconductors would offer efficient ¿-ray detection at or near ambient temperatures with energy resolution significantly better than NaI (T1) scintillators. For use at X-ray energies, this goal has been achieved with both HgI2, CdTe, and GaAs detectors. However, at higher energies (~660 keV) all current detectors have one or more significant deficiencies in terms of attainable volume, charge collection efficiency, and polarization effects. Starting with first principles, all potential compounds which can be formed by the binary combination of elements from the periodic chart were considered as possible detector materials. A rank-ordered listing of the most promising materials for further development is given as well as an assessment of the prospects for future success.

Theory of intense electromagnetic pulse propagation through the atmosphere

A set of fluid equations is derived to describe the interaction of a very strong electromagnetic pulse with a weakly ionized plasma. These equations are used to investigate the dynamic behavior of an intense electromagnetic pulse propagating through the atmosphere. Results show that the amount of energy transmitted through the medium depends very strongly on the initial energy of the pulse and such characteristics and its frequency, its shape, and its length. In addition, a pulse was propagated through an air filled waveguide to verify the acuracy of the theoretical model. The theory also predicts very accurately the pulse breakdown threshold.

Theoretical Band Structure Analysis on Possible High-Z Detector Materials

Theoretical energy band structure calculations have been utilized to investigate several high-Z materials for potential use as ambient temperature radiation detectors. Using the pseudopotential technique, the band structure for HgI2 has been determined and the effective masses of the holes and electrons have been estimated. Theoretical mobilities of the electrons and holes as a function of temperature have been computed for HgI2 and CdTe and are compared to experimental data.

Observation of stimulated emission in the near ultraviolet from a molecular beam epitaxy grown GaN film on sapphire in a vertical-cavity, single pass configuration

We report the first observation of stimulated emission from a GaN film grown by ion‐assisted molecular beam epitaxy. The observed near‐UV optical emission power was a nonlinear function of the pump power density. The characteristics of the observed stimulated emission are similar to those observed recently from films grown with low‐pressure metalorganic chemical vapor deposition techniques.

Propagation of intense microwave pulses in air and in a waveguide

The state of research on intense electromagnetic pulse propagation in air and in waveguides is reviewed. Some results obtained from recent investigations of the propagation of intense electromagnetic pulses in the atmosphere and in an air-filled waveguide when the field strength is above the threshold for air breakdown are presented. It is shown how the air breakdown affects the shape of the pulse. In addition, the accuracy of the calculational models is discussed, comparing calculations with experimental data. >

ALSB as a High-Energy Photon Detector

The possibility of using AlSb as a potential material for high-energy photon detection is examined by comparing the mobilities of the free carriers, the energy gap, the atomic number, and the carrier recombination time for AlSb, CdTe, Si, and Ge. It is concluded that at room temperature AlSb should be an intrinsically better high-energy photon detector than the three other materials. Simulated detector spectra for AlSb and CdTe are compared for ambient temperature detector performance.

The two-photon transition in indirect-band-gap semiconductors

Abstract The absorption coefficient of the two-photon excitation process in which phonons of the crystals participate during the transition process is calculated for ionic and covalent indirect-band-gap semiconductors. It is shown that this absorption coefficient can reduce to a form which can readily be used to estimate the absorption coefficient for a number of crystals if we use certain approximations. A numerical example was carried out for the GaP crystal. This calculation shows that both the optical phonon-assisted and the acoustical phonon-assisted two-photon absorption coefficients are within the same order of magnitude.

Two-photon indirect transition in GaP crystal

Abstract The two-photon indirect transition in n-type GaP crystals was investigated through transmission measurements at 1.17 eV. The value of the two-photon indirect coefficient was found to be approximately 1.7 × 10 -3 cm / MW , which is in close agreement with theoretical calculations.

Hall effect in reactively sputtered Cu2S

The Hall effect in thin films of reactively sputtered Cu2S was measured at temperatures from 90 to 300 °K. The hole concentration ranged from 1018 to 2×1019 cm−3. The hole mobility ranged from 5.5 to 9 cm2/V s. The predominant scattering mechanisms are ionized impurity scattering at T<100 °K and optical phonon scattering at T≳100 °K.

CALCULATIONS OF TWO‐PHOTON CONDUCTIVITY IN SEMICONDUCTORS

The photoconductivity produced in some direct‐band‐gap semiconductors by the two‐photon absorption process is investigated theoretically and found to be a very complicated function of the crystal parameters, the excitation photon energy, and the light excitation intensity. An application of the theory to a GaAs crystal is carried out.