Effect of modulation-doping on luminescence properties of plasma assisted MBE-grown GaN/AIGaN quantum well

In order to improve the crystal quality of GaN-based light emitting devices, photoluminescence (PL) characterization of below-gap states in plasma assisted MBE-grown GaN/AlGaN quantum well (QW) structures has been done by utilizing a below-gap excitation (BGE) light in addition to an above-gap excitation light. The decrease of the band-edge PL intensity due to the addition of the BGE of 1.17 eV indicates the presence of an energy-matched below-gap state in the two-wavelength excited PL. In continuation to our previous efficiency improvement by applying modulation-doping to GaAs/AlGaAs QW's. we focused on several undopcd and Si-doped GaN/AlGaN QW's. Experimental results showed that Si modulation-doping reduces the density of below-gap states in the QW region, hence it is promising for increasing internal quantum efficiency of GaN-based QW's

Heterostructure field effect transistor types with novel gate dielectrics.

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Influence of Surface Treatments on DC-Performance of GaN-Based HFETs

This work reports on the influence of the surface and the gate length on the performance of AlGaN/GaN based Hetero Field Effect Transistors (HFETs). Differently NH4Sx treated surfaces result in variation of the drain current IDmax of more then 100%. Gate recessing by photoelectrochemical treatment changes the threshold voltage Vth but affects the drain current little. Next, the reduction of the gate length increases the IDmax further by more than 60%. The IDmax values for the transistors are 350 mA mm––1 for the NH4Sx-treated, 850 mA for the untreated, and 1.43 A mm––1 for the one with a 0.2 mm gate length. The corresponding transconductances gm are 66, 150, and 280 mS mm––1, respectively. Surface analysis with Auger Electron Spectroscopy (AES) and contact characterization (TLM) reveals, that the NH4Sx treatment removes the native oxide and increases the contact resistance as well. Therefore we attribute the increase of IDmax and gm mainly to a beneficial behavior of gallium-oxide at the surface on the sheet carrier density nS of the 2DEG at the heterointerface