Si-CdS heterojunction memory diodes

The I-V characterisitcs of pSi-nCdS heterojunction diodes have been investigated, the diodes being fabricated by growing epitaxial CdS films on silicon substrates under UHV conditions. Under certain fabrication conditions, viz., a substrate-acceptor doping ∼1019 cm−3, a CdS film resistivity ∼102Ω cm, and Schottky contacts to the CdS, it has been observed that the diode possesses two resistance states. For one of the states, the high-resistance state, the current is an exponential function of bias voltage, whereas for the other, the low-resistance state, the current is a linear function of voltage. Switching from the high to the low state occurs with a few V reverse bias applied to the heterojunction and will remain in this state with the bias voltage reduced to zero, and remain thus for a few weeks, i.e., no hold-on voltage is required. To revert to the high state, a forward-bias voltage is applied to the heterojunction and the diode switches to its initial state when a circuit current of a few mA flows. A binary-memory array of pSi-nCdS diodes has been constructed with a bit density ≳103 cm−2, and when operated under pulsed-bias conditions, continuous switching at 5×103 Hz has been obtained and the number of switching cycles ∼107 before any degradation takes place. A descriptive model of the diode has been developed which attempts to show that trap defects within the CdS film are responsible for the memory and switching characteristics.

Hali tarjima qilinmagan