Semiconductor Gratings Research Articles

Electron wave diffraction by semiconductor gratings: Rigorous analysis and design parameters

An exact rigorous coupled-wave analysis has been developed to model ballistic electron wave diffraction by gratings with periodic effective mass and/or potential energy variations. Design expressions have been derived to calculate diffracted angles, to identify evanescent orders, and to identify the Bragg condition. Design expressions for Bragg regime (up to 100% diffraction efficiency in a single order) and Raman–Nath regime (high diffraction efficiency divided among multiple orders) diffraction are presented along with example Ga1−xAlxAs grating designs. Design procedures for ballistic electron switches, multiplexers, spectrometers, and electron waveguide couplers are described.

Far-infrared frequency shifting by optically induced gratings in semiconductors

A first approach to frequency shifting of far-infrared radiation by optically induced “moving” refractive index gratings in semiconductors is reported. The factors determining the performance of this frequency shifting technique are inferred using a one-dimensional analytical model. In a proof-of-principle experiment frequency shifting of 119 μm radiation was observed up to 80 MHz using a 300 mW, 488 nm Ar + laser for optical excitation.

Laser-induced grating self-diffraction from a medium with induced absorption

There are a great variety of optical nonlinearities that can lead to the phenomenon of laser-induced gratings (LIG) in semiconductors. In the present contribution the dynamic behaviour of an induced absorber with intrinsic bistability is investigated under excitation in a LIG self-diffraction arrangement. Using CdS as a model substance, the comparison of our theoretical model with our experimental findings gives an insight into the nonlinear dynamics of the degenerate carrier system and also an estimation of the transport properties of the electron-hole plasma.

Frequency shift and change in the spectrum of picosecond light pulses scattered by optically induced gratings in semiconductors

The first experimental observations were made of the frequency shift and of the change in the spectral composition of picosecond light pulses scattered by optically induced gratings in semiconductors. The observed effect is attributed to the time dependence of the refractive index and to the formation of a nonequilibrium electron-hole plasma.

Crystallographic Effects on the Photoelectrochemical Etching of Gratings in Compound Semiconductors

AbstractGrooves have been etched photoelectrochemically into a (100) n-GaAs surface using a 100 cycle/mm grating mask to define the illuminated area. The degree of mask undercutting and the shape of the groove bottom are shown to be functions of doping density and crystallographic orientation. High doping density gives rise to reduced undercutting, presumably due to a lesser extent of surface diffusion of photogenerated holes.

Ambipolar diffusion measurements in semiconductors using nonlinear transient gratings

The theory of self-diffraction of light by transient free-carrier gratings in semiconductors has been expanded to the case in which nonlinear absorption of light creates the grating. Its application to the experiments performed allowed determination of the free-carrier ambipolar diffusion coefficients in CdS, CdSe, and ZnSe crystals, and the mechanism of free-carrier recombination and carrier lifetime in CdS at low temperatures.