Silicon thin film space charge limited (SCL) diodes and SCL MOS transistors

Space charge limited semi-conductor devices possess significant advantages over conventional semiconductor devices mainly with respect to low noise properties, relative temperature insensitivity, and high frequency capability. The main problem in fabricating these devices in the past has been associated with the lack of a suitable high resistivity semiconductor material in a form amenable to the fabrication of high quality stable devices. Such a material is now available. This material is high resistivity silicon (>100 ohm. cm.) in the form of thin (< 1 micron) single crystal layers epitaxially deposited on a single crystal insulating substrates (sapphire). Device characteristics obtained initially on SCL devices fabricated in these thin high resistivity silicon films have been presented. Subsequent device investigations have resulted in the successful fabrication of a variety of single and double carrier thin film SCL devices. These devices include: 1. Single carrier SCL resistors. 2. Single carrier SCL surface barrier diodes. 3. Double carrier SCL diffused diodes. 4. Single carrier thin film SCL MOS transistors. 5. Double carrier thin film SCL MOS transistors. The characteristics of the two thermal devices show the classicI . \alpha V^{2}characteristic expected for these solid state devices (analogous to Child's law for vacuum, i.e.I \alpha V^{3/2}). Current densities as high as 20,000 amps/squ. cm. have been obtained under DC conditions due to the novel device structures used. These device structures will be described and the device design theories will be presented and compared with the device characteristics actually obtained on the above devices.