Growth and characterization of high-speed InP/InGaAs bipolar transistors using n+-InP contacting layers

CBE growth with an elemental Si dopant source has produced InP/InGaAs single heterojunction bipolar transistors (HBTs) with excellent high frequency results. However, the reaction of metal-organics with the hot solid source dopant has lead to anomalous doping behavior which may have an effect on the reproducibility of the growth. As an alternative, gaseous SiBr₄ has been demonstrated as a highly efficient n-type dopant source for InGaAs and InP while maintaining excellent morphology. Using this source, CBE grown InP/InGaAs HBTs have been demonstrated. Yet, difficulties exist when using SiBr₄ doped InGaAs in the collector/subcollector region in that X-ray diffraction indicates that the lattice constant of InGaAs decreases with increasing SiBr₄ flow. This dependence leads to increased difficulty in the growth of Si-doped InGaAs since the shift in lattice constant has to be accounted for prior to growth. From a device standpoint, the use of a thick InGaAs layer for the collector/subcollector region may degrade HBT device performance due its low thermal conductivity. For integration of a p-i-n photodetector with an HBT by using the base/collector/subcollector regions, the n-type InGaAs layer detracts from the performance of the detector by allowing absorption of incident photons outside the active region of the device, thereby adding to the noise of the device and decreasing the speed of the response. By using heavily SiBr₄ doped InP contacting layers, these problems can be avoided since InP shows no lattice shift with doping while it maintains a high thermal conductivity