Physical processes in cadmium sulphide space charge limited dielectric diodes

Physical processes in the space charge limited In-CdS-Au dielectric diode have been studied. Measurements of incremental capacitance show that in the majority of diodes a Schottky barrier exists at the collector contact. The fixed space-charge density in the depletion layer is uniform and corresponds to a total donor density generally in the range 10 16 to 10 17 cm -3 . Measurements of current-voltage characteristics are consistent; elimination of the Schottky barrier at large forward bias enables the Mott-Gurney square law to be observed whereas enhancement of the barrier at large reverse bias enables field emission of electrons to occur from the collector contact into the conduction band of the crystal. The majority of measurements indicate a contact potential step for electrons at the collector in the range 1.0 to 1.4 eV. Measurements of current noise have been carried out over the frequency range 1 kc/s to 200 Mc/s. At low frequencies the noise spectrum is dominated by an approximately inverse frequency variation which is markedly structure sensitive. At high frequencies however noise drops well below the shot noise level and approaches the thermal (Nyquist) noise level thus confirming that space-charge reduction mechanisms are operating.