B. Tell

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.

Temperature dependence of GaAs‐AlGaAs vertical cavity surface emitting lasers

The temperature performance of GaAs‐AlGaAs vertical cavity surface emitting lasers has been studied from 60 to −160 °C. A minimum threshold current occurs considerably below room‐temperature where the wavelength of the Fabry–Perot resonance of the cavity matches the wavelength of the maximum gain of the active region. The laser quantum efficiency increases for decreasing temperature, exhibiting a change of slope near the temperature of the threshold minimum.

Fast nonlinear optical response from proton‐bombarded multiple quantum well structures

Proton bombardment is shown to shorten the recovery time of the excitonic absorption in GaAs/GaAlAs multiple quantum well saturable absorbers. The response time can be reduced from 30 ns to 150 ps without affecting the absorption characteristics or the saturation energy.

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.

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.

Femtosecond excitonic optoelectronics

The authors discuss a novel approach to femtosecond optoelectronics which uses the excitonic response to electric fields as a detector and the excitonic nonlinear response to optical fields as a generator. The sensitivity of the quantum-well exciton to applied electric fields is used to measure electrical transients with femtosecond time resolution. The authors examine several mechanisms for femtosecond electrical pulse generation, including exciton ionization and two-photon absorption, and present measurements of the propagation properties of coplanar striplines on ultrathin semiconductor substrates in the 1-100-THz frequency range. The generation and detection of an electrical pulse with a 180-fs risetime propagating on a coplanar stripline on GaAs/AlGaAs quantum wells are demonstrated. >

Visible Stimulated Emission in Ternary Chalcopyrite Sulfides and Selenides

We report the observation of stimulated emission in four I‐III‐VI2 chalcopyrite sulfides and selenides AgGaS2, CuGaS2, AgGaSe2, and CuInS2 spanning the visible spectrum from 4650 to 8200 A. CuGaS2 and CuInS2 can readily be prepared p type, and p‐n junctions have been formed in CuInS2.

Electrochemichromic cells based on phosphotungstic acid

We report a new material for self‐contained all‐solid‐state electrochromic devices with fast response. The material is phosphotungstic acid (PWA) which, at room temperature, is both an electrochromic material and an ionic conductor. Response times of 50 msec have been measured in cells of type M/PWA/SnO2, where M denotes an electrode that provides ions of Ag, Cu, or Li. The cell exhibits memory.

Motion of p‐n junctions in CuInSe2

We report the first p‐n junction delineation and diffusion study in a ternary chalcopyrite‐type semiconductor. p‐n junctions were formed in Zn‐ or Cd‐plated p‐CuInSe2 by 5‐min anneals at 200–450 °C. By means of angle lapping and staining techniques, junction depths xj varying from ∼1 μm to ∼130 μm were determined. These measurements yield the relationship lnxj (μm) =14.31−6900/T (K). The interdiffusion coefficient derived from xj is D (cm2/sec) =164 exp[−1.19 (eV)/kT]. The large preexponential term indicates concentrations or mobilities of point defects substantially above those of the related II‐VI compounds.

Electrical properties of CuGaS2

A series of CuGaS2 crystals were annealed in excess sulfur at temperatures between 250 and 850°C. This treatment varies the room‐temperature hole density from 5 × 1015 cm−3 to 2 × 1018 cm−3. From the temperature dependence of the resistivity, the acceptor ionization energies of several representative samples were determined. The energy increases from 5 to 70 meV as a function of increasing resistivity.