Indium arsenide tunnel diodes

Abstract

The tunnel-current density through a very narrow p-n junction depends exponentially on the reduced effective mass of the charge carriers and the bandgap. Therefore, indium arsenide appears to be a promising material for fast tunnel diodes at room temperature ( m r⋍0·05 , E g⋍0·33 eV), giving higher frequency limits for a given doping level or lower doping (lower capacity) for a given gain-bandwidth product. Tunnel diodes have been made by alloying InCd and InZn dots on InAs crystals which had been doped with 2 × 10 16 to 6 × 10 18 Te atoms/cm 3. The resulting I–V characteristics vary with doping level and temperature from classical p-n curves to Esaki curves of 10:1 peak to valley current ratios. The best ratios at room temperature are about 2:1. Good units with high current density do not show any structure indicative of phonon participation. However, lower-current units do show two conductance minima in the rising part of the forward characteristic at 4°K. The high-current units also show a different temperature dependence of the peak current and of the peak voltage than those of lower current density. This leads to the tentative conclusion that the characteristics of the low-current units are determined by phonon-assisted tunneling, while in the high-current units the direct tunneling process is dominant. In the I–V characteristic of units made from low-doped material an interesting cusp structure is found. This resembles the “phonon” structure above, but is dependent on the surface condition of the diode. A measurement of the rise time of a switching pulse across the diode proved to be limited by the circuit to 10 −9 sec. This and other indirect measurements allow an estimate of a gain-bandwidth product, for the faster diodes, of 3 kMc/s.