C. E. C. Wood

Complex free‐carrier profile synthesis by ’’atomic‐plane’’ doping of MBE GaAs

Doping solely during periods when growth was suspended has been used to synthesize profiles not easily achieved by conventional doping techniques. Suspension of growth under arsenic stabilized conditions allows Ge doping to produce n‐type complex profiles with reduced autocompensation. At higher temperatures, autocompensation becomes apparent. Under gallium stabilized conditions, heavily autocompensated n‐type layers resulted, consistent with a nonunity incorporation coefficient.

Surface and interface depletion corrections to free carrier-density determinations by hall measurements

Errors in the determination of (ND-NA) for semiconductor epitaxial layers by the Hall method can result if corrections for carrier depletion are omitted in the calculations. Simple practical procedures are discussed to correct for carrier depletion that occurs in epitaxial layers at their free surfaces, and their interfaces with semi-insulating substrates. Theoretical estimates of carrier depletion in GaAs indicate that depletion regions can extend several microns into high purity epitaxial layers, and can cause (ND-NA) to be considerably underestimated. Experimental evidence is presented in support of the theory.

Magnesium‐ and calcium‐doping behavior in molecular‐beam epitaxial III‐V compounds

Residence lifetimes of Mg on GaAs surfaces were observed using 10 KV reflection electron diffraction and Auger electron spectroscopy to decrease from ∼120 s at 550 °C to ∼1 s at 600 °C. The electrical incorporation coefficient is ∼0.3 at and below 500 °C decreasing to ∼3×10−4 at 600 °C at the expense of desorption. Hole mobilities of uniformly Mg‐doped samples are as good as those for equivalently Be‐doped GaAs samples. Calcium does not behave as a shallow acceptor in GaAs grown by molecular‐beam epitaxy.

Growth of Sb and InSb by molecular‐beam epitaxy

The temperature dependence of the surface lifetime of free antimony on InSb has been determined using 10‐kV reflection electron diffraction (RHEED). A desorption activation energy was extracted from these data and found to have a value of 64.2±3 K cal/mole which is within experimental error of ΔH (sublimation) for monatomic Sb. At substrate temperatures of 280 °C, it was possible to nucleate antimony in an epitaxial relationship with (111)A‐ and (111)B‐oriented InSb surfaces; subsequent epitaxial growth could continue at temperatures as low as 40 °C. Films of InSb were grown homoepitaxially on (111)A‐, (111)B‐, and (001)‐oriented InSb substrates and heteroepitaxially on (001)‐oriented InAs and GaAs over a wide temperature range, 280 °<T<450 °C. Surface‐atom reconstructions for Sb‐stabilized and In‐stabilized films are identified.

Photoluminescence of AlxGa1−xAs grown by molecular beam epitaxy

Reduction of background oxygen containing species, higher substrate temperature, and low arsenic fluxes during growth have all been found critical to improve the luminescence of molecular beam epitaxy AlxGa1−xAs alloys. Attention to these parameters has allowed greatly improved quality films to be grown which show strong exciton recombination for the first time. The main unintentional acceptor impurity was then found to be carbon.

Crystal orientation dependence of silicon autocompensation in molecular beam epitaxial gallium arsenide

Silicon‐doped GaAs has been grown simultaneously on (100), (110), and (111)B oriented GaAs substrates by molecular beam epitaxy. For constant Si, Ga, and As4 fluxes the surface morphology of the (110) and (111)B faces degraded with increasing substrate temperature above ∼500 °C. (100) films had an n‐type free‐electron concentration of 5×1016 cm−3 independent of substrate temperature. Films on (110) substrates were p type when grown above ∼550 °C and n type below ∼550 °C whereas (111)B films were highly resisitive under most growth conditions. Low‐temperature (4 K) photoluminescence showed good correlation between the Si acceptor peak heights and the compensation ratios derived from electrical measurements.

Arsenic stabilization of InP substrates for growth of GaxIn1−xAs layers by molecular beam epitaxy

A new method of cleaning InP substrates under molecular beam epitaxy conditions involving heating to ⩾500 °C in an As4 flux (JAs4 ≃1015–1016 cm−2 s−1) is described. Evidence of surface cleanliness, good morphology, ordered surface reconstruction, and integrity of chemical composition at the interface is given. Lattice‐matched layers of Ga0.47In0.53As grown on InP substrates cleaned in this way showed excellent electrical properties: e.g. a room‐temperature mobility μ300=8600 cmPu2 V−1 s−1 at n300 =1016 cm−3.

GaInAs‐AlInAs structures grown by molecular beam epitaxy

Growth of GaInAs and A1InAs by molecular beam epitaxy on idium phosphide substrates is reported. Unintentionally doped, closely lattice matched GaInAs layers were n‐type with μ300 up to 8800 cm2 V−1 s−1 and n as low as 1×1016 cm−3 whereas undoped A1InAs layers were typically high resistance. 2‐MeV Rutherford backscattering showed good GaInAs crystal quality although the A1InAs was somewhat disordered. Evidence for cation exchange at interfaces and surface accumulation of indium was evident from both RBS and sputter Auger profiles. In situ grown A1 films on A1InAs showed an effective barrier height∼0.8 eV from 1/C2 V s V curves, however attention to the forward I‐V characteristics indicated lower values. DLTS results indicate the GaInAs to be virtually trap‐free but that A1InAs has high deep level concentrations owing to low growth temperatures. Good photoluminescent efficiencies were demonstrated for GaInAs layers, however, poor results were obtained for A1InAs.

On the origin and elimination of macroscopic defects in MBE films

Abstract Spitting of group III metal droplets from Knudsen type effusion cells has been found culpable for a genre of problematical macroscopic surface topographical defects observed in the growth of semiconductor films by molecular beam epitaxy. Successful precautions are described which virtually eliminate the problem.

Indium antimonide‐bismuth compositions grown by molecular beam epitaxy

Thin films of InSb‐InBi solid solutions have been prepared by molecular beam epitaxy. Using in situ reflection electron diffraction, conditions for epitaxial growth of stoichiometric layers were established on (001) and (110) surfaces of both InSb and GaAs wafers. Bi is shown to modify the diffraction patterns of (001) InSb from C(8×2) and (√2×√2) 45° to (1×3). Surface residence times of Bi were found indefinitely long (≳10 min) at temperatures ?420 °C. Bi incorporation into InSb during growth by molecular beam epitaxy is strongly dependent on Bi surface concentration, and influenced by substrate temperature and surface nonstoichiometry. Secondary ion mass spectrometry depth profiling and 2.5 MeV ion dechanneling spectra showed that ∼3% Bi can be incorporated substitutionally in Sb sites, under In rich growth conditions (largest available concentration of VSb sites). Increased Bi surface accumulation and interstitial incorporation are observed under Sb‐rich surface conditions and as the relative flux of B...