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A model is developed for the incorporation of donors and acceptors in epitaxial GaAs which indicates that the thin p‐type region often observed at the layer‐substrate interface in n−p+ structures is caused by the electric field associated with surface states and substrate doping. The model also predicts impurity gradients at the outer surface, about which little is known experimentally. Since results from the model are in agreement with many experimental observations, surface states and substrate doping are believed to be the major cause of impurity gradients in epitaxial GaAs.

Column‐IV (Si, Ge, and Sn) and column‐VI (S, Se, and Te) impurities are used to dope high‐purity layers of vapor epitaxial GaAs. Resistivity and Hall data on a large number of samples show that the common donors in GaAs (assumed to be column‐IV impurities on gallium sites and column‐VI impurities on arsenic sites) are compensated by acceptor centers which are donor impurity‐vacancy complexes. These acceptor complexes are tentatively identified as column‐IV impurities on gallium sites associated with single gallium vacancies and column‐VI impurities on arsenic sites associated with single arsenic vacancies.

We have developed a model of Cr in GaAs which is consistent with a large body of experimental data. It relies or recent spectroscopic models and on our interpretation of redistribution and electrical data, all of which indicate the existence of Cr complexes. The existence of rapidly diffusing interstitial Cr donors is assumed and justified. The model offers a unified picture of the effects of implantation on the Cr profile. It contains mechanisms for compensation and redistribution, which offer an explanation of the semi-insulating properties of Cr doped GaAs and of the two apparently incompatible classes of diffusion and anneal data. The redistribution depends on how the Cr was incorporated and on the vacancy concentration profiles. A study of representatives of the two classes of redistribution data allows us to estimate a lower limit of interstitial Cr diffusion constant and of the vacancy diffusion lengths in GaAs.

Using back reflection Laue measurements we have examined the substrate orientation dependence of antiphase domain boundaries for ZnSnP2 (c= 2a) grown on GaAs by liquid phase epitaxy. These results together with those of other workers indicate that {211} substrates are best for the growth of chalcopyrite layers withc= 2a, while {100} substrates are best for those chalcopyrites withc

The chalcopyrite alloy ZnxCd1−xSnP2 is a potentially use-ful electronic material. In addition to having effective masses lower than and energy gaps similar to its III-V compound analogs, this alloy can also be lattice matched to InP. We have used an open-tube, sliding-boat, liquid-phase system to grow ZnxCd1−xSnP2 epitaxially on InP sub-strates. Unintentionally-doped layers have electron con-centrations as high as 3 × 1019cm−3 with mobility values of about 2,000 cm2/V-sec. These mobility values are sub-stantially larger than have been obtained in the equivalent III-V materials at similar concentrations.

The distribution of impurities incorporated in epitaxial layers during their growth is determined by diffusion due to concentration gradients and by drift in the built-in electric field. This problem has been previously treated in the approximation that the impurities reach their equilibrium distribution during growth. We have extended this calculation to treat impurity drift and diffusion under non-equilibrium conditions, a situation much more characteristic of most realistic growth condi-tions. In the new calculation, the solution of the Shockley-Poisson problem is exact and the boundary con-dition at the growth interface is an approximation based on the electrostatics of surface states. The new calcu-lation also permits consideration of outdiffusion from the substrate, a phenomenon of technological significance. It is also capable of modeling variations of source im-purity concentration and growth rate during epitaxial growth. Calculations modeling n-type GaAs epitaxy of practical interest are presented.

The preparation of single‐crystal GaAsP by halide vapor transport is described. That dislocation free GaAsP can be achieved was verified experimentally for whiskers grown by the vapor‐liquid‐solid method. In the growth of monocrystalline ingots for device purposes, growth mechanics and the resulting crystal habit are strongly influenced by degenerate Zn, Te, and Se doping. Since n‐type crystals require higher supersaturations, single‐crystal growth is easier to obtain with Zn doping.The as‐grown dislocation structure of ingots with low‐index natural facets is examined by decoration and etching. Typical densities are 5×103 to 106/cm2. From their simple crystallographic orientations different dislocations are identified. 〈211〉, {111} and 〈100〉, {110} edge dislocations are observed in {110} polygonization walls. Values of mobility and carrier density are evaluated from a device point of view. Laser diodes with threshold currents as low as 3000 A/cm2 at 33.3% GaP have been obtained from this material.

Zero‐bias Schottky barrier capacitance measurements indicate the presence of heavily‐doped surface impurity gradients in n‐type epitaxial layers of GaAs grown on n+ substrates. These impurity gradients are produced during epitaxial growth by the electric field due to 5×1011 cm−2 surface states in GaAs in 1000 K. For n‐type layers grown on Cr‐doped substrates, high‐resistance regions are observed at the surface. These regions are probably caused by the buildup of positively charged chromium atoms in the electric field at the surface. The redistribution of chromium atoms in ion‐implanted samples during annealing can also be explained by electric fields due to surface states and the implanted‐ion profiles.

Below band‐gap photovoltaic response with a half‐power point at 1.31 eV is observed in p‐type In1−xGaxP on n‐type GaAs heterojunctions with {111} interfaces. This response is apparently due to photon‐assisted tunneling of carriers across the interfacial energy gap, which is smaller than the energy gaps of the constituent materials. The same mechanism can be employed in other heterojunctions with appropriate energy‐band lineups to obtain longer wavelength infrared response.

Integrated structures consisting of a double‐heterostructure GaAs‐AlGaAs etched‐mesa Fabry‐Perot laser coupled to a high‐purity GaAs waveguide have been fabricated and tested. Room‐temperature threshold current densities as low as 7.5 kA/cm2 for 1‐μm‐thick active layers were measured.

Photothermal ionization measurements on Si‐doped GaAs grown by molecular beam epitaxy (MBE) have indicated that the previous identification of the Si donor peak was incorrect. Data leading to the new identification are presented and the results leading to the earlier identification are re‐examined. Implications of the new identification for the importance of Si as a residual donor in epitaxial GaAs grown by various techniques are discussed.

GaAs electroabsorption avalanche photodiodes in n‐n+ GaAs waveguides have been used to detect the 1.06‐μm radiation from a Nd : YAG laser with a responsivity of 125 A/W and an internal quantum efficiency of 23%. The response at this wavelength is due to a combination of band‐to‐band and defect‐to‐band electroabsorption.

We have measured the lasing energy of optically pumped high‐purity GaAs from 2 to 300 K. Low‐temperature results show strong many‐body effects in the band‐to‐band lasing below the single‐particle band‐gap energy, and the high‐temperature data indicate that the lasing energy approaches the band gap measured by photoconductivity.

A high‐purity GaAs sample with a measured room‐temperature mobility of 15 200 cm2/V sec is examined in detail. Resistivity and Hall measurements are in reasonable agreement with a previously developed model which shows that conducting inhomogeneities can result in anomalously high measured mobilities. A sizeable number of precipitates (probably gallium) are observed in the sample.

Uniform avalanche Schottky barrier photodiodes have been fabricated by plating a thin layer of platinum on GaAs and forming a guard ring by proton radiation. Operating at a gain of 100 these photodiodes exhibit gain‐bandwidth products greater than 50 GHz and enhanced signal to noise ratio in excess of 30 dB. The observed variation on the spectral response with bias can be accounted for by a change in the absorption of the Schottky barrier diode.

Although a number of mechanisms have been proposed to explain the existence of impurity gradients in epitaxial GaAs, the impurity gradient model presented in this report shows that such effects are inherent to the growth process. That is, when the carrier concentrations in the substrate, growing layer, and at the growth surface are different at the growth temperature, non-uniform time-dependent electric fields are obtained in the layer. These fields can enhance or retard the motion of ionized impurities and defects during growth producing impurity gradients at the outer surface and different conductivity regions at the epitaxy-substrate interface. High temperature resistivity and Hall coefficient measurements were made on epitaxial layers and substrates and analyzed using a self-consistent four-band model to obtain quantitative results for the impurity gradient model for growth on heavily-doped n-type substrates predicts that thin (0.05 micrometers or larger) p-type regions at the epitaxy-substrate interface will be produced under conditions commonly encountered in the epitaxial growth of GaAs.