The δ-Doped In0.25Ga0.75As/GaAs Pseudomorphic High Electron Mobility Transistor Structures Prepared by Low-Pressure Metal Organic Chemical Vapor Deposition*

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Abstract
The (800 Å)GaAs/In0.25Ga0.75As/(0.5 µm) GaAs strain layers with δ-doping in the GaAs cap layer were fabricated without using AlGaAs layers. Triethylgallium (TEG), trimethylindium (TMI), arsine (AsH3) and silane (SiH4) were used as the sources and dopants in these structures grown by the low-pressure metalorganic chemical vapor deposition (LP-MOCVD) technique for the first time to study these structures. The δ-doping was obtained by a stop-growth process by which a very thin and heavily doped layer (1.86×1013 cm-2) can be realized. For the (δ-doped) GaAs/In0.25Ga0.75As/GaAs high electron mobility transistor (HEMT) structures, the concentration of two-dimensional electron gas (2-DEG) and the Hall mobilities were investigated. Experimental results show that a structure with (80 Å) In0.25Ga0.75As as the active channel and with a 70 Å spacer layer revealed the highest 2-DEG concentration and mobility product of 5.5times1016 V-1·s-1 at a temperature of 77 K. These structures are easy to achieve by the LP-MOCVD mechod and are promising for high-performance field effect transistors (FETs).