InP-based double heterojunction bipolar transistors(DHBTs) are well suited to high-speed integrated circuit applications due to their superior electron transport properties of the materials and sufficient breakdown voltages. The latter is achieved through using the InP material in the collector, which forms the second heterojunction with the InGaAs base. The figures of merit of mircowave performances of HBTs are $f_{T}$(current-gain cutoff frequency) and $f_{max}$(maximum oscillation frequency). Generally, for integrated circuit applications operating at high frequency ranges, a balanced high $f_{T}$ and $f_{max}$ are required. In this work, design methods of the DHBTs with both high $f_{T}$ and $f_{max}$ were investigated through the approximate expressions of $f_{T}$ and $f_{max}$. Then, the simulations of $f_{T}$ and $f_{max}$ were performed based on incorporating the physical parameters of epitaxial layers and layout dimensions into equivalent small signal elements. Especially, reduction of base-collector capacitace by etching the InP collector laterally were found to be very important to obtain high $f_{max}$.
In this thesis, the emitter fingers of the DHBTs were aligned to the [01$\bar{1}$] direction which is reported to have superior reliability. But, following this emitter direction, lateral etching of the InP collector is not almost achieved. In order to overcome this problem, for the first time, a new Lateral Reverse-etching(LRE) technique is proposed and established. To our knowledge, there has been no reports of removing InP collector with the [01$\bar{1}$] emitter direction through wet chemical etching.
The fabricated LRE-DHBT with a $0.8×10\mum^{2}$ emitter area showed offset voltage $V_{CE}$,offset of 0.1V, DC current gain h_{FE} of 48, collector ideality factor $n_{C}$=1.02 and base ideality factor $n_{B}$=1.37. The comparison of the collector-emitter breakdown voltages($BV_{CEO}$=6.55V of the DHBTs with 300nm-total collector thickness and $BV_{CEO}$=5.7V of the SHBTs with 600nm-total collector thickness) showed sufficiently high breakdown voltage property of the DHTs. The Microwave performances of the fabricated LRE-DHBT with a $0.8×10\mum^{2}$ emitter area were measured on-wafer from 0.5 GHz to 20 GHz using a 8720C Network Analyzer. The peak $f_{max}$ and $f_{T}$, estimated from -20dB/decade extrapolation, were 172 GHz and 120 GHz at Ic=14.2mA and Vce = 2V, respectively. For verification of the validity of this technique, the devices with the same emitter dimension without the LRE technique were also measured and compared. The peak fmax and $f_{T}$ of the conventional DHBT without the LRE technique were 122 GHz and 104 GHz, respectively. The LRE technique has been found to enhance $f_{max}$ of the device appreciably(41% increase). From the measured S-parameters and small signal modeling, the Cbc values of the LRE and conventional DHBTs were extracted to be 19fF and 34.83fF, respectively. The $C_{bc}$ decrease of 46% of the fabricated LRE-DHBT has been found to be achieved by the LRE technique. A new Lateral Reverse-etching technique has been found to increase $f_{max}$ of DHBTs appreciably.
