Schottky Barrier Structure Research Articles

Pinning Action of a Thin Ga Interfacial Layer in an Sb/Ga/GaAs Schottky Barrier Structure Grown by MBE

AbstractThe pinning action on the barrier height of a Ga interfacial layer in an Sb/Ga/GaAs structure prepared by molecular beam epitaxy has been tracked as a function of Ga layer thicknesses for both n and p-GaAs (100). The barrier height ÆBn for n-type GaAs (ND=3×1015cm−3), determined by thermal activation measurements and capacitance measurements, changes from 0.8 to 1.0 eV as the Ga layer is increased from zero to three monolayers. The barrier height ÆBp for p-type GaAs decreases in a converse fashion so that the sum ÆBn + ÆBp is equal to the GaAs energy gap. Up to a Ga layer thickness of about one monolayer the barrier height changes are about linearly proportional to thickness.The action seen is compatible with barrier height changes that are seen when Sb/GaAs junctions are prepared with the original surface alternatively As or Ga rich and subjected to thermal annealing at temperatures up to 250°C.

Optical and electrical properties of amorphous silicon films prepared by photochemical vapor deposition

Amorphous silicon films have been prepared through mercury-photosensitized decomposition of monosilane gas at low temperatures. The films show optical and electrical properties comparable with those of the best films prepared by plasma chemical vapor deposition. The feasibility of amorphous solar cells with short-circuit current densities of more than 10 mA/cm2 has been demonstrated by fabrication of a Schottky barrier structure.

Deposition and properties of zinc phosphide films

Thin films of zinc phosphide have been deposited on tungsten-coated steel substrates at 400–600 °C by the reaction of zinc and phosphine in a hydrogen atmosphere; tungsten was used as a barrier against the diffusion of iron from the substrate into zinc phosphide. By using a proper PH3/Zn molar ratio, the deposited films have been identified by electron microprobe and x-ray diffraction techniques to be Zn3P2. The electrical resistivity and photovoltage of unintentionally doped zinc phosphide films were measured as a function of the composition of the reaction mixture. The effective intragrain minority carrier diffusion length in nearly stoichiometric films was measured by the scanned beam method using a Schottky barrier structure. The incorporation of dopants into zinc phosphide films was also explored.

Cadmium telluride films on foreign substrates

Thin films of cadmium telluride have been deposited on mullite and tungsten-coated graphite substrates at 500–700 °C by the direct combination of cadmium and tellurium in a hydrogen atmosphere. Their microstructure and crystallographic properties were studied. The importance of controlling the Cd/Te molar ratio in the reaction mixture to obtain nearly stoichiometric films was demonstrated. The electrical properties of nonstoichiometric and nearly stoichiometric films on mullite substrates were measured by the van der Pauw technique. Schottky barriers were used to measure the electrical properties of cadmium telluride films on W/graphite substrates. The effective intragrain minority carrier diffusion length in n-type films was measured by the scanned electron beam method using a Schottky barrier structure.

HgTe/CdTe heterojunctions: A lattice-matched Schottky barrier structure

HgTe-CdTe lattice-matched heterojunctions were formed by the epitaxial growth of HgTe on CdTe substrates using a low-temperature metal organic chemical vapor deposition technique. These heterojunctions combine features of the Schottky barrier structure, due to the high carrier concentrations found in the semimetallic HgTe, with the structural perfection present in a lattice-matched heterojunction. The measured Schottky barrier height varied from 0.65 to 0.92 eV depending on the details of the heterojunction growth procedure used. This dependence may be due to the formation of an inversion layer in the CdTe at the interface. Presence of such an inversion layer suggests that the valence band discontinuity between HgTe and CdTe is small, in agreement with previous theoretical estimates.

An assessment of the suitability of rf sputtered amorphous hydrogenated Si as a potential solar cell material

We review several material properties thought to be important for the production of high efficiency amorphous semi-conductor Schottky barrier solar cells, with particular reference to a systematic study made in this laboratory of amorphous Si:H alloys prepared by rf sputtering. These requirements include: (a) an optical gap which efficiently absorbs the solar spectrum in a thin film, (b) a Fermi level position close to the conduction band for a large work function difference between metal and semiconductor, (c) high photoconductivity, (d) long carrier migration lengths, and (e) a low overall density of gap states. Using our data on these electronic properties, we show that we can satisfy these conditions somewhat by depositing at an argon pressure of 20 mTorr. Furthermore, we demonstrate, using a simple Schottky barrier structure, that significant improvements in device performance are achieved, particularly in open circuit voltage, as the above properties are optimized. Other factors which might still limit the performance of the device are discussed, and from an examination of the temperature dependence of the short circuit current, we conclude that the most likely to be important is the “effective” diffusion length for valence band holes.

Schottky barrier on W-GaAs contact

Tungsten is deposited on GaAs by WCl6 reaction with H2. The GaAs substrate is heated to 400 °C during the deposition. The forward current of W-n-GaAs structures prepared in such way increases exponentially over five decades in accordance with the theory of the thermionic electron emission from the semiconductor to the metal. The Schottky barrier height is obtained from the I–U and the C–U measurements and in both the cases it is (0.81 ± 0.01) eV. The reverse current is connected with the generation current in the space-charge region of the GaAs Schottky barrier structure. [Russian Text Ignored]

Experimental Evidence of Hot-Electron Transport through Thin Metal Films

The metal-base triode sandwich was used to measure the current transfer ratio in a Schottky barrier structure. The transfer ratio is discussed considering two distinct current types—that through base metal and that through pinholes. An electron-phonon mean free path of 125 Å and an electron-electron mean free path of 230 Å (at 0.7 eV) were measured. An investigation of the structure of very thin Al and Au films deposited on Al2O3 was made by transmission electron microscopy. Al films were found to be more continuous than Au films of comparable thickness.

Integrated-circuit Schottky polarity guard

An aluminium Schottky-diode bridge, fabricated using a standard linear integrated-circuit process, is described. The Schottky-barrier structure effectively eliminates parasitic p-n-p transistor action, which is troublesome when collector-base diodes are used. A ‘guard-ring’ geometry enables a reverse breakdown of 70 V to be achieved. Comparable devices made with ‘metal-overlap’ geometry have reduced breakdowns of 36 V. A further advantage of using Schottky diodes in the bridge is their low forward drop, which for this device is 0.42 V at 10 mA. The intended area of application is in hybrid microcircuits for telephone sets.