ENHANCEMENT OF 2DEG DENSITY IN GAAS/INGAAS/ALGAAS DOUBLE HETEROJUNCTION POWER MODFET STRUCTURES BY BURIED SUPERLATTICE AND BURIED P + -GAAS BUFFER LAYERS.

The structures were grown by MBE (molecular-beam epitaxy) in the following sequences on semi-insulating substrates: GaAs buffer/high barrier buffer/n** plus -GaAs/In//0//. //1//5Ga//0//. //8//5As/n** plus -Al//0//. //3Ga//0//. //7As/n** plus -GaAs. The high barrier buffer layers were made of either a AlGaAs/GaAs superlattice or a buried atomically planar beryllium-doped P** plus -GaAs layer. A reference layer with an undoped GaAs buffer layer was also grown for comparison. A high extrinsic dc g//m of 408 mS/mm and a full channel current of 610 mA/mm at room temperature are obtained for 1. 2- mu m-gate-length FETs with buried buffer layers; FETs without the buried high barrier layers could not be pinched off. An f//T of 21. 5 GHz and an f//m//a//x of 80 GHz are extrapolated from measured S-parameter data from 0. 5 to 26. 5 GHz with a 6-dB/octave slope. A 2DEG (two-dimensional electron gas) sheet charge density as high as 1. 7 multiplied by 10**1**2/cm**2 has been obtained before the onset of parasitic conduction in the AlGaAs layers, while Hall data indicates larger densities. Preliminary CW power measurements show 0. 45 W/mm with 11-dB linear gain and 36% power-added efficiency at 10 GHz and 0. 36 W/mm with 7-dB linear gain and 22% efficiency at 18 GHz.