A germanium space-charge-limited triode

An experimental solid-state triode directly analogous to a vacuum-tube triode is described. Control and modulation of the flow of space-charge-limited (SCL) electron currents in germanium have been achieved by inserting a control electrode into an n+πn+ solid-state diode. This electrode consists of a set of closely spaced p+ stripes that are capacitively coupled with the emitter and collector. Results indicate that the control electrode modulates the current flow in a manner analogous to that of the grid electrode in a vacuum-tube triode. The SCL current obeys the three-halves power law as predicted for a field-dependent mobility of the form where 0 is the low field mobility and Ecthe critical electric field. An analysis of the I-V characteristics of the fabricated solid-state triodes reveals that these structures are capable of exhibiting a high transconductance, a large amplification factor, and an input impedance greater than a megohm. An important advantage of such a device is a potentially low noise figure as predicted by theory. Other attractive features of the device, such as a low sensitivity to temperature changes and an expected high frequency response, will also be discussed.