J. L. Shay

Room‐Temperature Electrical Properties of Ten I‐III‐VI2 Semiconductors

The room‐temperature electrical properties of ten I‐III‐VI2 (I=Cu, Ag; III=Al, Ga, In; VI=S, Se) compounds are presented. The resistivities of eight of these compounds are rapidly changed by annealing under maximum and minimum chalcogen pressures. The Cu compounds can readily be made p type, a feature lacking in the analogous II‐VI compounds. However, the Cu compounds with energy gaps of 1.7 eV or above have not been made n type.

CuInSe2/CdS heterojunction photovoltaic detectors

We report CuInSe2/CdS p‐n heterojunction photovoltaic detectors which display uniform quantum efficiencies of up to ∼70% between 0.55 and 1.25 μ. Response times as short as 5 nsec have been observed. A weak electroluminescence (0.01% external quantum efficiency) peaking near 1.4 μ has also been observed at room temperature.

Efficient CuInSe2/CdS solar cells

We report the preparation of a CuInSe2/CdS heterojunction solar cell having a solar power conversion efficiency of 12% measured on a clear day in New Jersey (∼92‐mW/cm2 solar intensity).

Heterojunction band discontinuities

The discontinuity ΔEc=0.56 eV in the conduction band edge at n‐CdS/p‐InP junctions is reported. This discontinuity and others are compared with photoemission data and with Van Vechten’s extension of these data to many tetrahedrally coordinated semiconductors. Agreement between measured discontinuities and theoretical predictions is very good. Predictions are made for band parameters pertinent to interfaces involving AIIBIVCV2 compounds with zinc blende, chalcopyrite, or wurtzite crystal structures.

Analysis of the electrical and luminescent properties of CuInSe2

We discuss the electrical properties and the luminescence spectra of CuInSe2 melt−grown single crystals as a function of the growth and annealing conditions, and the presence of extrinsic dopants such as Zn or Cd. We find that crystals grown from melts containing a slight Se excess or annealed under maximum Se pressure are p type, whereas crystals grown from excess In melts or annealed under minimum Se pressure (vacuum) are n type. The low−temperature photoluminescence spectra of crystals as−grown or annealed between 400 and 700 °C are characteristic of the conductivity type. At 77 °K, p−type crystals emit in a band peaked at 1.00 eV (type A spectrum), whereas the emission of n−type crystals peaks at 0.93 eV (type B spectrum). Types A and B spectra can be interchanged by alternate anneals in minimum or maximum Se pressure. Type B emission dominates the electroluminescence spectrum of p−n junctions. A sharp band−to−band emission at 1.04 eV is present in the 77 °K photoluminescence spectrum of some high−res...

Electrochromism in anodic iridium oxide films

The oxidation state of iridium ions in an oxide film grown electrochemically on an Ir metal reflector electrode in aqueous 0.5M H2SO4 electrolyte can be rapidly and reversibly modulated by voltage pulses of 1 V amplitude according to the reaction: Ir(OH)n(transparent) ⇄IrOx(OH)n−x(colored)+xH++xe. This valency interconversion produces a marked change in light absorption throughout the visible wavelength region and occurs without change in film thickness. Color‐bleach cycles exhibit reflectance contrast changes, ΔR/R, and charging times, τ, suitable for electrochromic display devices, e.g., for a film 700 A thick: ΔR/R=60% at λ=546 nm and τ≈40 msec. The fast write‐erase times are made possible by the highly porous and hydrated nature of the oxide film. The charge (∼20 mC cm−2) and energy (∼20 mJ cm−2) are comparable with those for other electrochromic oxide systems, e.g., the tungsten bronzes. Advantages of the iridium oxide system include: (i) fast response; (ii) stability of the colored written state in ...

p−InP/n−CdS solar cells and photovoltaic detectors

We have prepared p−InP/n−CdS heterodiode photovoltaic detectors with a uniform quantum efficiency of ∼70% for wavelengths between 550 and 910 nm. On a cloudy day in New Jersey, (53 mW/cm2) solar power conversion efficiencies of 12.5% have been measured on cells provided with antireflection coatings.

Green electroluminescence from CdS–CuGaS2 heterodiodes

Heterodiodes have been prepared by vapor‐deposition expitaxy of n‐type CdS on p‐type CuGaS2. Typical diodes emit green light under forward bias with external quantum efficiencies of 0.1% at 77 °K and 0.001% at room temperature. The radiative recombination results from electron injection into the CuGaS2.

Liquid encapsulated czochralski pulling of InP crystals

The growth of bulk indium phosphide crystals via liquid encapsulated Czochralski pulling from both stoichiometric and nonstoichiometric melts is described. Nominally un-doped crystals with carrier concentration ND-NA = 6 × 1015 cm−3 and Hall mobilities of 4510 cm2/Vsec at room temperature were grown. Also, we prepared Zn-or Cd-doped p-type crystals in the range 1016 ≤ NA-ND ≤ 1018 cm−3 with Hall mobilities ≤ 130 cm2/Vsec and Sn-doped n-type crystals in the range 4 × 1017 ≤ NA-ND ≤ 1018 cm-3 with Hall mobilities ≤ 2400 cm2/Vsec. The dislocation density of LEC pulled InP crystals is typically ~ 104 cm−2.

Junction electroluminescence in CuInSe2

We report the first observation of homojunction electroluminescence in CuInS2. These homojunctions are made by two different annealing procedures which convert a surface layer of p−type crystals. Diodes made by low−temperature (200 °C) In−Ga diffusion show a rectification ratio of 17000:1 at 2 V and a zero bias resistance of 1×107 Ω. For diodes made by high−temperature (600 °C) annealing in InCl3 the values are 15000:1 and 3×107 Ω, respectively. Electroluminescence has been observed in diodes made by In−Ga diffusion. The spectrum peaks at 1.48 eV at 300 °K and at 1.42 eV at 77 °K. The internal quantum efficiency is 10−5 at 300 °K and 10−3 at 77 °K.