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The performance of AlGaN/GaN high-electronmobility transistors (HEMTs) on diamond and SiC substrates is examined. We demonstrate GaN-on-diamond transistors with periphery W G = 250 µm, exhibiting f t = 27.4 GHz and yielding a power density of 2.79 W/mm at 10 GHz. Additionally, the temperature rise in similar devices on diamond and SiC substrates is reported. To the best of our knowledge, these represent the highest frequency of operation and first-reported thermal and X -band power measurements of GaN-on-diamond HEMTs.Index Terms-GaN on diamond, high-electron-mobility transistor (HEMT), microwave power, thermal effects in AlGaN, X -band.

A large number of novel devices have been recently demonstrated using wafer fusion to integrate materials with different lattice constants. In many cases, devices created using this technique have shown dramatic improvements over those which maintain a single lattice constant. We present device results and characterizations of the fused interface between several groups of materials.

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The valence and conduction band discontinuities for the lattice matched (Ga,In)P/GaAs heterojunction have been determined by capacitance-voltage (C-V) profiling. Both p-p and n-n heterojunctions were profiled, in order to obtain separate and independent values for both the valence-band-edge discontinuity (ΔEv) and the conduction-band discontinuity (ΔEc). The band lineup is found to be of the straddling type with the valence- and conduction-band discontinuities 0.24 and 0.22 eV, respectively, with an estimated accuracy of ±10 meV. Computer reconstruction of the C-V profiles was used to check the consistency of the data. The band offset data indicate that the (Ga,In)P/(Al,Ga)As system should be staggered for a certain range of Al compositions.

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