Abstract

We report the fabrication and characterization of the InGaP/GaAs single het­erojunction bipolar transistor (SHBT). The cross sectional structure of the studied device is shown in Fig.l. The SHBT with a delta-doped sheet located at the E-B heterointerface (delta-SHBT) exhibits a common-emitter current gain as high as 410 and an extremely low offset voltage of only 55 mV. Figure 2(a) and (b) illustrate the I-V characteristics and the expanded view near the near of the same device. The higher current gain of delta-SHBT can be attributed to the increase of the hole barrier resulting from the delta-doped sheet and to the reduction of charge storage because of the existence of thin spacer (50-A). The low offset voltage is due to the elimination of the potential spike of E-B junction. The calculated conduction band-edge dia­grams near the E-B junction of delta-SHBT, conventional SHBT and HEBT at various biased conditions are plotted in Fig.3. At equilibrium, no potential spike exists for all the three structures. As Vbe= + 1.0 V forward biased, a potential spike about 60 meV existed in an SHBT while no potential spike existed in both delta-SHBT and HEBT. Also notice that the width of neutral region in narrow energy-gap emitter for an HEBT is also increased with biased voltage. It is evident that the potential spike do be eliminated by utilizing delta-doped sheet. On the other hand, calculated increase of the E-B capacitance for our delta-SHBT is very small due to the thin enough delta-doped sheet.