Specific contact resistivity of InGaAs/InP p-isotype heterojunctions

The authors have examined a possible, important source of parasitic resistance in InP/InGaAs and other heterojunction devices. They have measured the specific resistance of the heterointerface between p-InGaAs and p-InP by means of a modified transmission-line model. It is found that the specific contact resistance, r/sub c/, of these structures increases dramatically when the current is forced to go through the heterointerface. The increase is most dramatic for light to medium doping on either side of the heterointerface. Higher doping reduces the increase, although it is still significant, even for very high doping levels. The effect of inserting a digitally graded bandgap layer between the contact and cladding layers was also investigated. It is found that the heterointerface r/sub c/ drops by an order of magnitude compared to that of the abrupt heterojunction case for the same doping in the contact and cladding layers. The results agree with a model based on thermionic emission. Therefore, very high doping and/or grading of this heterojunction is necessary to obtain very low series resistance in detectors and lasers.<>