G. Haacke

New figure of merit for transparent conductors

A figure of merit for transparent electrode materials has been defined by φTC=T10/Rs, where T is the optical transmission and Rs is the electrical sheet resistance. Expressions are derived to predict the transparent electrode properties of a material from its fundamental electrical and optical constants. The performance of thin metal films is compared to semiconducting oxide coatings.

Metalorganic chemical vapor deposition of high-purity GaAs using tertiarybutylarsine

The growth of high‐purity gallium arsenide using tertiarybutylarsine (TBA) and trimethylgallium is reported. The availability of high‐purity TBA has permitted the growth of material with liquid‐nitrogen mobilities of up to 80 000 cm2/V s, the highest value yet reported for growth with any alkyl arsine. The residual donor species have been identified by magnetophotoluminescence.

Preparation and Semiconducting Properties of Cd3P2

Single and polycrystalline samples of Cd3P2 have been prepared. Undoped samples are n‐type with carrier concentrations between 1017 and 1018 cm−3. The thermoelectric power of these samples goes up to −170 μV/°C at 300°K. Mobility values up to 3000 cm2/V sec at 300°K were measured. The mobility of single crystals varies in the extrinsic range near room temperature proportionally to T−1.1 (T is temperature). Optical measurements indicate an optical band gap of approximately 0.5 eV. The results of annealing experiments support the assumption that the high electron concentration of undoped samples is due to phosphorus vacancies. The doping properties of various elements have been studied. Copper introduces what is probably a deep‐lying acceptor level, but p‐type samples could not be obtained.

Epitaxial growth of high‐mobility GaAs using tertiarybutylarsine and triethylgallium

Epitaxial layers of nominally undoped GaAs have been grown by metalorganic chemical vapor deposition using liquid tertiarybutylarsine and triethylgallium. n‐type layers were obtained having total residual shallow acceptor concentrations of ∼1013 cm−3 and Hall mobilities comparable to those obtained with arsine and triethylgallium in the same reactor. Liquid‐nitrogen Hall mobilities up to 116 000 cm2 /V s were observed.

Electrical Transport in FeCr2S4‐CuCr2S4 Spinels

Thermoelectric power α, electrical conductivity σ, and Hall effect have been studied for single crystals of the Fe1−xCuxCr2S4 system. While FeCr2S4 is a p‐type semiconductor, substitution of Fe by Cu causes n‐type conduction between x∼0.2 and x∼0.5 in the temperature range 4.2°–550°K. For x>0.5, p‐type conductivity is observed. An explanation of the experiments is given on the basis of a three‐band model.

Carbon acceptor incorporation in GaAs grown by metalorganic chemical vapor deposition: Arsine versus tertiarybutylarsine

Undoped p‐type GaAs epilayers were grown by low‐pressure metalorganic chemical vapor deposition (MOCVD) at 650 °C and 76 Torr using either arsine or tertiarybutylarsine (TBA), and trimethylgallium (TMG). Extremely high‐purity precursors were used in order to eliminate extrinsic doping effects. Carbon acceptors from the TMG were the dominant residual electrical impurities under all growth conditions. Temperature‐dependent Hall measurements were used to make a quantitative comparison of the carbon acceptor concentrations for arsine‐ and TBA‐grown epilayers over a range of As partial pressures. For a given group V partial pressure, we report a significant reduction in carbon acceptor incorporation using TBA compared with arsine under identical growth conditions.

Magnetophotoluminescence characterization of residual donors in GaAs grown by metalorganic chemical vapor deposition

The residual donor species in undoped GaAs epilayers grown by metalorganic chemical vapor deposition have been characterized by magnetophotoluminescence (MPL) measurements at high magnetic fields (7 T). Most samples were grown using trimethylgallium and arsine, but samples grown using the liquid group‐V source t‐butylarsine were also studied. The results show good agreement with identifications previously made in high‐purity samples (NA+ND≤5×1014 cm−3) at zero magnetic field, but with greatly improved spectral resolution and signal levels. With the MPL technique, residual donor species were resolved even in relatively impure samples (NA+ND=1×1016) for which no information was obtained at zero magnetic field. For the samples grown with arsine, Ge donors were observed to predominate in the high‐purity samples, but Si was the dominant donor in the lower‐purity samples. The Si impurity was traced to contamination from a quartz baffle in the growth chamber. Lower levels of sulfur donors were observed in many s...

Anomalous Thermal Conductivity of Cd3As2 and the Cd3As2−Zn3As2 Alloys

The room‐temperature lattice thermal conductivity of Zn3As2 is 0.012 W/cm·°C; that of Cd3As2 is 0.014 W/cm·°C or less. Anomalously low thermal conductivities (as much as 30% below calculated values) are found for samples of Cd3As2 and Cd‐rich alloys of Cd3As2 with Zn3As2 where the electrical conductivity is high (>103 Ω−1 cm−1). Thermal conductivities for Cd3As2 samples fall into two groups: Samples doped with an element which is expected to enter the anion sublattice have normal thermal conductivities, while undoped samples or those doped with an element which should enter the cation sublattice tend to have anomalously low thermal conductivities. High electron mobilities and general lack of correlation of carrier concentration with thermal conductivity indicate that the anomaly is not in the electronic component of thermal conductivity. Instead, doping experiments, as well as the temperature dependencies of thermal conductivities indicate that the anomaly is entirely in the lattice component and is due t...

Residual donor and acceptor incorporation in InP grown using trimethylindium and tertiarybutylphosphine

Residual donor and acceptor species were studied in a series of high purity n‐type InP epilayers grown by metalorganic chemical vapor deposition using tertiarybutylphosphine and trimethylindium (TMIn). Over the entire range of growth conditions, the residual donors were found to be S and Si using magnetophotoluminescence spectroscopy. These designations agreed with the observed dependence of the transport data on growth conditions. Residual levels of Zn and Mg or Be acceptors were identified by photoluminescence (PL) measurements at low excitation powers. C acceptors were below the limits of detection by PL, as in other studies using phosphine and TMIn.

Sources of donor impurities in undoped GaAs grown using arsine and trimethylgallium

Magnetophotoluminescence spectroscopy (MPL) has been used to ascertain the source of donor impurities in high‐purity GaAs grown by atmospheric pressure metalorganic vapor deposition using arsine and trimethylgallium. A linear correlation between absolute MPL intensity and net carrier concentration for high‐purity n‐type epilayers over the concentration range 1×1014–2×1015 cm−3 provided an unambiguous method for identifying the source of donor impurities by comparing epilayers grown with different source batches. Batch‐to‐batch variations in the quality of films grown with eight different arsine cylinders were traced directly to the presence of varying amounts of a Ge‐containing contaminant in the arsine.