F/sub max/ enhancement in InP-based DHBTs using a new lateral reverse-etching technique

A new lateral reverse-etching technique, developed for the InP DHBTs with emitters aligned to the [011~] direction which is well known to be more reliable than the other directions, is proposed and demonstrated. Two highly doped InGaAs and InP layers are utilized to alleviate the difficulty of lateral etching due to very little lateral etch rate along this direction. The DHBT with a 1.5/spl times/10 /spl mu/m/sup 2/ emitter size fabricated using this new method shows greatly improved peak f/sub max/ of 172 GHz and peak f/sub T/ of 120 GHz. From comparisons of microwave performance of the two devices which are fabricated with and without the new method, a 41% increase of f/sub max/ and a 45% reduction of base-collector junction capacitance have been achieved. Therefore, it has been verified that the proposed new method is very effective to considerably improve f/sub max/ by reducing the base-collector junction capacitance.