Emission processes of the interaction between the quantum well and donor delta layer in heterostructures for pHEMTs

Abstract

We present experimental and theoretical investigations of pHEMT heterostructures with AlGaAs/InGaAs/GaAsquantum wells (QWs) and/or a delta-doped layer, which can be used as active regions in transistors operating in the4–18 GHz frequency range. Using the electrochemical capacitance-voltage setup ECV Pro we, for the first time, experimentallyobserved a concentration peak from the near-surface delta layer of the pHEMT structure together with apeak of QW enrichment. The capacitance of the electrolyte-semiconductor contact was measured by Agilent LCR-meter,which was connected to the electrochemical cell of ECV Pro through a specially designed relay module. Using numericalsimulation of the electronic characteristics of nanoheterostructures by self-consistent solution of Schrödinger and Poissonequations we determined electrostatic potential profiles for band edges, band offsets, quantum-confinement levels, andconcentration profiles of charge carriers for the samples under investigation. The impact of delta-layer position on theconfined energy levels and carrier concentration in the QW was experimentally and theoretically analyzed in detail. Wedetermined the optimal distance between the QW and delta layer, which provides the most efficient process of supplyof charge carriers to the QW. The conducted work is directed at improvement of SHF devices, allowing one to increasethe gain coefficient and transconductance of transistors.