E. Buehler

LINEAR AND NONLINEAR OPTICAL PROPERTIES OF ZnGeP2 AND CdSe

The refractive indices of ZnGeP2, point group 42m, have been determined from 0.64 to 12 μ. ZnGeP2 has positive birefringence with reasonable temperature tunability and a band gap in the visible. Its nonlinear optical coefficient d14 for second harmonic generation (SHG) measured relative to d14 of GaAs is 0.83 ± 15%. The birefringence of ZnGeP2 is not large enough to allow phase‐matched SHG, but nondegenerate phase‐matched three‐frequency mixing is possible and the parametric oscillator threshold power is calculated for several situations. A redetermination of the coefficient d31 in CdSe is made and the materials compared. It is concluded that ZnGeP2 may be a most promising material for parametric generation in the 0.8– to 12‐μ region.

Evidence for low surface recombination velocity on n‐type InP

A comparison was made of the photoluminescent (PL) intensities of n‐type InP and GaAs at room temperature. The PL intensity for InP was over 100 times greater than for comparably doped GaAs. The effect of surface recombination velocity S on the PL intensity was evaluated numerically. When this evaluation is applied to the PL intensity ratios of n‐type InP and GaAs it shows that S for n‐type InP is sufficiently small to eliminate significant influence of nonradiative surface recombination on the observed PL intensity.

Linear and nonlinear optical properties of ternary A II B IV C 2 V chalcopyrite semiconductors

The refractive indices of ZnSiAs 2 , CdGeP 2 , and CdGeAs 2 have been determined over a wide range of wavelengths and the optical nonlinear coefficient for second-harmonic generation from the 10.6-μ CO 2 laser have been measured. The absorption coefficient versus wavelength is given for the above materials as well as for ZnGeP 2 , a previously discussed material. Three-frequency phase-matched mixing is described for each material.

Phase‐matched submillimeter wave generation by difference‐frequency mixing in ZnGeP2

Using two step‐tunable CO2 lasers, we have observed phase‐matched generation of frequencies 70 <ν<110 cm−1 by nonlinear mixing in a birefringent ternary semiconductor, ZnGeP2. An observed power of ∼1.7 μW at 83.37 cm−1 gave a signal‐to‐noise ratio of ∼1000 with a Ge:Ga detector. In combination with tunable optical lasers, this technique should yield a tunable source of submillimeter wave radiation for high‐resolution spectroscopy.

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.

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.

CdSnP2–InP heterodiodes for near‐infrared light‐emitting diodes and photovoltaic detectors

Heterodiodes have been prepared by liquid‐phase epitaxy of n‐type CdSnP2 from Sn solution onto p‐type InP. Electroluminescence is observed near 1.4 μ with internal quantum efficiencies of 10% at 77°K and 1% at room temperature. The photovoltaic response of typical diodes shows moderate quantum efficiencies (4–12%) in the near infrared (1.2–1.0 μ).

PHASE‐MATCHED UP CONVERSION OF 10.6‐μ RADIATION IN ZnGeP2

Phase‐matched sum mixing of 10.6‐ and 1.06‐μ radiation has been observed at near normal to the optic axis in ZnGeP2. Its theoretical performance as a 10.6‐μ detector via up conversion compares favorably with direct detection by a cooled Ge:Hg photoconductive detector. The sum‐mixing efficiency of ZnGeP2 is 140 times superior to that of Ag3AsS3, the next best material. The large angular aperture resulting from θm ≃ 90° indicates that the material will be useful for image up conversion.

Preparation and properties of InP/CdS solar cells

We describe the preparation and properties of the recently reported InP/CdS single‐crystal solar cells having a solar power conversion efficiency of 12.5%. We also describe a process for increasing the efficiency of these and inadvertently inferior cells to 14%. The ultimate efficiency achievable with InP/CdS using state‐of‐the‐art liquid‐encapsulated Czochralski p‐type InP substrates is calculated to be 17.2% for AM2 conditions and 14.0% for AM0 conditions.

Polycrystalline thin‐film InP/CdS solar cell

We report the preparation of a polycrystalline thin‐film InP/CdS solar cell of area 0.52 mm2 having a power conversion efficiency of 2.8% under AM1 conditions. Based on the current‐voltage characteristics, we estimate that development of an improved contact to the p‐type InP would result in substantially higher efficiencies without any further improvement in the InP/CdS interface.