IMPROVED INVERTED ALINGA GAINAS 2-DIMENSIONAL ELECTRON-GAS STRUCTURESFOR HIGH-QUALITY PSEUDOMORPHIC DOUBLE-HETEROJUNCTION ALINAS/GAINAS HIGH-ELECTRON-MOBILITY TRANSISTOR DEVICES/

Molecular beam epitaxy grown AlInAs/GaInAs single quantum well high el ectron mobility transistor structures (SQW-HEMT) on InP were developed for transistor applications with high current drive capability. Use o f low growth temperatures for the layers below the GaInAs channel in c ase of the inverted interface proved to be essential to achieve simult aneously high electron concentrations in the channel region and mobili ties equal to those of normal single heterojunction HEMT structures. T he mobilities obtained in SQW-HEMT structures which employed Si delta- doping on both sides of the SQW channel were found to be only weakly d ependent on the channel thickness down to 16 nm whereas below the mobi lity tended to degrade. Based on theoretical calculations an optimum s patial distribution of the carriers is deduced aiming at high channel electron density and low parallel concentration in the lower supply re gion by optimizing the thickness of the spacers and the asymmetric dis tribution of the donors above and below the channel. Further improveme nts of the SQW-HEMT structures were obtained by incorporating elastica lly strained In-rich channels. In this way, increased mobilities and c oncomitantly enhanced electron concentrations have been achieved. Unsu rpassed 77 K mobilities amounting up to 55.000 cm(2)/V s in conjunctio n with a Hall carrier density of 6.0 X 10(12) cm(-2), which compares w ith a simulated channel density of 5.4 X 10(12) cm(-2), were attained. 0.6 mu m gate length devices fabricated on the optimized SQW-HEMT lay er structures clearly demonstrate the superior performance of the SQW design in terms of saturation current without compromising the pinch-o ff behavior.