Measurement of Electron Free Lifetime and Trapping Factor in High Purity Cadmium Sulfide, Cadmium Sulfide/Selenide and Cadmium Selenide Using the Method of Ultrasonic Amplification

摘要

Cadmium sulfide, cadmium sulfide/selenide, and cadmium selenide were studied in an effort to arrive at estimates of several electron transport parameters. Electron free lifetimes, trapping factors, and effective drift mobility were all deduced from direct measurement of the variation of stress wave gain with applied electric field and Hall mobility. Attempts to isolate the characteristic energy level structure of high quality amplifier crystals were made by means of photoconductivity and absorption measurements at both 77K and 300K. These methods, in general, failed to indicate any peculiarities which could be readily correlated with amplifier performance. The one exception, a sample of CdS compensated in selenium, showed a severe decrease in slope and a broadening of the primary absorption edge. During attempts to compensate CdS in flowing oxygen, it was discovered that 3 mm. cubic crystals formed on that portion of the CdS directly exposed to the oxygen source. X-ray powder measurements confirmed that these crystals were CdO.