Emitter size effects and recombination at the emitter periphery in self-aligned InP/GaAsSb/InP DHBTs

Surface recombination effects are studied in both non-self-aligned and self-aligned NpN InP/GaAsSb/InP unpassivated DHBTs down to sub-micrometer emitter dimensions. The present study is motivated by the drive to scale InP DHBTs for higher speeds and integration densities. Self-aligned InP/GaAsSb/InP DHBTs are characterized by weak emitter size effects (ESEs), and periphery recombination currents are found to be very nearly identical to published results for InP/GaInAs SHBTs despite the major differences in emitter junction band alignments ("type-II" vs. "type-I") and emitter injection mechanisms (thermal vs. hot election injection). The correspondence of measured periphery currents in both systems indicates that ESEs are dominated by a mechanism common to InP/GaAsSb and InP/GaInAs devices: this requirement is fulfilled by the direct electron injection from the InP emitter mesa sidewalls onto the extrinsic base surface