| Research Abstract |
Our researches consisted of following two terms.
1.Emitter structure for extraction of electrons by buried nano-metal-wires as gate
We fabricated hot electron transistors with buried nano-metal -wires to extract ion of electron. In DC characteristics, saturated I-V characteristics was confirmed.
To suppress current injection from emitter to gate, new structure was invented (patent applied for) and ratio between emitter current vs. gate current was enhanced to several tens. Estimated transconductance was 10 mS from obserbed DC charactarisrtics.
To reduce scattering of electron, purity of InP intrinsic layer was confirmed. As a result, electron mobility of 110,000 cm^2/Vs at 77 K was confirmed in AlInAs/InP HEMT structure, When Si-doped layer was eliminated, electron mobility of 220,000 cm^2/Vs at 77K was confirmed. To our knowledge, these mobility at 77K was world records. Thus high purity of our materials was confirmed.
2.Collector structure by buried nano-metal-wire.
Through study through crystal growth, we found that thickness of over layer on wires was changed by the number of wires. Because failure of crystal growth was due to this phenomena, we fabricated the structure with only one wire as a collector with refinement of crystal growth conditions. As a result, we fabricated HBT with one nano^metal wire as collector. In this device, the emitter area was 0.1μm×0.5μm. To our knowledge, this area was smallest as heterojunction bipolar transistors. Smallest total collector capacitance was also confirmed.
As a contact resistance, emitter contact resistivity was reduced from 3x10^<-6>Wcm^2 to 1x10^<-6>Wcm^2 and base contact resistivity was reduced from 2.5x10^<-6>Wcm^2 to 3x10^<-7>Wcm^2 by change of electrode material (from titanium to pallsdium). This reduction combined with small collector capacitance is very important to obtain good microwave performance.
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