Preparation and Properties of Nonheat-Treated Single Crystal Cu[sub 2]S-CdS Heterojunctions

Abstract

The photoelectronic properties of single‐crystal Cu2S‐normalCdS heterojunctions have been investigated. The heterojunctions were formed on the A or Bfaces of conducting normalCdS single crystals by dipping in a cuprous chloride solution at 75°C. No separate heat‐treatment was given. The cells typically had monochromatic quantum efficiencies greater than 10% in the region 0.5–0.9micro;. The photoresponse is due to carrier pair generation in the Cu2S , with transfer of electrons across the interface into the normalCdS . The forward current at and below room temperature is dominated by tunneling of electrons through interface states. A general band diagram of the heterojunction is discussed. Consistent differences in the behavior of A and Bface samples were noted with respect to the growth kinetics of the Cu2S , the maximum photovoltage at 300°K, the I–V characteristics, and the junction capacitance. The effect of uniaxial stress on the capacitance of A and Bface samples suggests a piezoelectric mechanism.

The Growth of, and the Formation of Grain Boundaries in, Cu2 S Films Grown on Faceted Single Crystal CdS Substrates

“…Grain boundaries are formed because the CufS (orthorhombic) and CdS (hexagonal) crystals belong to different crystal systems. That the Cu2S grows at different rates (1,(15)(16)(17) with different morphologies is also confirmed. This has important implications for the manufacture of Cu2S-CdS cells using a rough CdS substrate because a CufS film of uniform thickness cannot be grown on it and the reflectivity of the different exprosed Cu2S surfaces can be different.…”

“…Some of the crystals were examined in an optical microscope and a SEM, and then the Cues was grown using the dipping technique described by Lindquist and Bube (17). Usually some of the crystal surfaces were protected with black wax, and they were dipped for times ranging from 5 m i n to 2 hr.…”

Bis(2,2'-biquinoline)copper(I) nitrate as an in situ spectrophotometric probe of cadmium sulfide/cuprous sulfide heterojunction formation

“…A noteworthy feature is the comparison of this rate to that for hot aqueous cuprous solutions. Rates in aqueous media are considerably faster with values of ~10""7 to 3 X 10™6 cm/s having been reported at comparable temperatures (4,14). Synthesis from amyl alcohol solutions of I would probably be most useful for controlled preparation of relatively thin (<10"5 cm) Cu2S layers.…”

“…In interpreting these kinetic results the measured initial rates should be treated as an average, since several different CdS crystallographic faces were exposed to the solution of I. Studies of CdS/Cu2S heterojunction formation in aqueous media have indicated that the rate of reaction can be dependent on the crystallographic face (14,15). If we assume uniform reactivity and a density for Cu2S of 5.6 g/cm3 (16), the reactions pictured in Figures 3-5 would correspond to an average Cu2S thickness of ~10™6 cm after 30 min.…”