Study of 1/f and 1/f Noise for InP DHBT

This work reports experimental data comparing the low frequency noise spectrum of InP based HBTs. Double heterojunction device structures are examined with and without surface passivation ledges. INTRODUCTION Compound semiconductor InP heterojunction bipolar transistors (HBTs) hold great promise for ultra high-speed analog microwave circuit applications. The low frequency noise characteristics of HBTs are of interest in the design of low phase noise microwave oscillators where such noise can be upconverted to near carrier frequencies and appear as phase noise. [1]-[2] In most HBTs, the generation-recombination current in the base-emitter junction and the exposed base surface are the dominant sources of 1/f noise. It has been shown that by using a thin depleted AlGaAs surface passivation ledge the 1/f noise of AlGaAs/GaAs HBTs can be significantly reduced, by as much as 17dB, through a reduction in base surface recombination. [3] However, because the recombination velocity of the InP/InGaAs system is much lower than in the AlGaAs/GaAs system, it is relevant to examine whether a similar result will be obtained for the InP/InGaAs system. This work examines low frequency noise characteristics of InP/InGaAs double heterojunction (DHBT) devices with and without surface passivation ledges. DEVICE STRUCTURE The devices used in this study were grown by commercial MBE on semi-insulating Fe-doped InP substrates. All devices used in this study had dimensions 2x10μm. Device layer structure information is shown in Table 1. Non-ledge devices have identical emitter, base, and collector layers, but do no have the etch stop and ledge. Ledge devices were fabricated using the double etch stop ledge (DESL) process. Non-ledge devices were have self aligned bases. TABLE I DEVICE LAYER STRUCTURE Layer Material Thickness Å Doping cm Emitter InP 750 5E+13 Etch Stop InGaAs 50 3E+17 Ledge InP 250 3E+17 Base InGaAs 550 3E+19 Collector InP 7,500 2E+17 sub-collector collector base sub-collector collector base ledge emitter