A smooth and monotonic potential energy gradient was established at a p-type (InGa)As--undopad InP heterojunction to efficiently transfer conduction electrons from the (InGa)As:p layer to the InP:.o slashed. layer. This potential energy gradient was established with a compositionally graded p-type semiconductor alloy layer and an n- type InP built-in field layer interposed at the heterojunction. The compositionally graded semiconductor alloy layer spatially distributes the conduction band discontinuity of the (InGa)As--InP heterojunction and the InP:n built-in field layer eliminates potential energy barriers from the conduction band over a wide range of externally-applied biases including no externally applied bias. The smooth and monotonic potential energy gradient thus established promotes efficient transfer of the conduction electrons due to drift from the (InGa)As:p layer to the large bandgap InP collector layer where they contribute to the output current of any number of electronic devices. The utility of this potential energy grading structure was demonstrated in a transferred-electron photocathode device wherein the efficient transfer of photoelectrons from the (InGa) As:p absorber layer to the InP:.o slashed. electron-transfer layer has been utilized. This structure has utility in a number of electronic devices requiring such electron transfer across an (InGa)As:p--InP:.o slashed. heterojunction including p-i-n photodetectors and heterojunction bipolar transistors.
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