Fmax 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 1.5×10 μm² emitter size fabricated using this new method shows greatly improved peak f_max of 172 GHz and peak f_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_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_max by reducing the base-collector junction capacitance.