Theoretical and experimental studies of the electron mobility and the free-carrier absorption of n-type InP were carried out in the temperature range 77–300 °K. All major scattering processes and screening effects were taken into consideration. It was found that the experimental dependence of electron mobility and free-carrier absorption on temperature and/or on carrier concentration can be consistently explained only when the effect of compensation is quantitatively taken into account. Convenient procedures are presented for the determination of the compensation ratio from the values of electron mobility and from the free-carrier absorption coefficient. The high contribution of optical-phonon scattering in InP limits the applicability of the free-carrier absorption approach to electron concentration n≳1017 cm−3. Electron mobility, however, can be reliably employed for the determination of the compensation ratio for n≳1017 cm−3 at 300 °K and n≳1015 cm−3 at 77 °K.

Theoretical calculations of electron mobility and free-carrier absorption in n-type GaAs at room temperature were carried out taking into consideration all major scattering processes. It was found that satisfactory agreement between theoretical and experimental results on free-carrier absorption is obtained only when the effect of compensation is quantitatively taken into account. In conjunction with experimental studies it is shown that the electron mobility (for n≳1015 cm−3) and free-carrier absorption (for n≳1016 cm−3) are sufficiently sensitive to the ionized impurity concentration to provide a reliable means for determining the compensation ratio. Convenient procedures are presented for the determination of the compensation ratio from the free-carrier absorption coefficient and from the computed values of room-temperature electron mobility. Values of the compensation ratio obtained by these two procedures are in good agreement provided the carrier-concentration variations in the material are not appreciably greater than 10%.

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A B S T R A C TIt was established that ideal, diffusion-controlled, steady-state segregation, never accomplished on earth, was achieved during the growth of Te-doped InSb crystals in Skylab. Surface tension effects led to nonwetting conditions u n d e r which free surface solidification took place in confined geometry. It was further found that, under forced contact conditions, surface tension effects led to the formation of surface ridges (not previously observed on earth) which isolated the growth system from its container. In addition, it was possi~ble, for the first time, to identify unambiguously: the origin of segregation discontinuities associated with facet growth, the mode of nucleation and propagation of rotational t w i n boundaries, and the specific effect of mechanical-shock perturbations on segregation. The results obtained prove the advantageous conditions provided by outer space. Thus, fundamental data on solidification thought to be unattainable on earth because of gravityinduced interference are now within reach.Structural and compositional control during solidification of materials is impeded by gravity-induced effects in the melt. Thermal gradients necessary for crystal growth lead, in the presence of gravitational forces, to thermal convection which in general causes uncontrolled variations in the solidification rate and in diffusion boundary layer thickness; such variations lead directly to periodic and/or random microscopic and macroscopic segregation inhomogeneities. F u rthermore, in the presence of gravity, establishing steep thermal gradients, frequently required to prevent constitutional supercooling, is often impossible and consequently interface breakdown is unavoidable.Gravity effects are, thus, primarily responsible for the present lack of reliable solidification data and the existing gap between theory and experiment. Consequently, crystal growth and associated segregation phenomena are still based on empiricism, and the properties and performance of solids are not at their theoretical limits.Gravity-free conditions made accessible through the space program provide a unique opportunity to obtain reliable crystal growth data and, therefore, to advance our quantitative understanding of solidification processes; in addition this program makes possible the exploration and assessment of the potential of outer space for materials processing.Indium antimonide was chosen for the presently reported Skylab experiment because its relatively low melting point (525~ made the experiment compatible with the available electrical power. In addition, chemical etching, the only high-resolution technique available, at the time, for the study of segregation inhomogeneities on a microscale, had been developed on InSb to its most advanced level.The experiments performed during the Skylab-III and -IV missions included the growth of undoped, tellurium-doped, and tin-doped indium antimonide. The present report is concerned primarily with results obtained on tellurium-doped InSb. ObjectivesThe objectives of...

Adsorption of O2 and H2O on GaAs exhibits a sharp contrast in behavior: O2 bonds to As sites almost exclusively while H2O predominantly bonds to Ga sites. The formation of Ga–OH bonds due to dissociative adsorption of H2O preceded by a molecular adsorption step is inferred from UPS data. Corroboration of these findings is provided by SIMS data for positive Ga and negative As ions. The role of hydrogen is discussed in the formation of stable oxides on the GaAs surface.