High frequency n-type MODFETs on ultra-thin virtual SiGe substrates

SiGe MODFETs on ultra-thin virtual substrates are presented. MBE grown 100 nm thick pseudomorphic Si0.7Ge0.3 layers have been relaxed by using He+ ions implanted approximately 100 nm below the hetero-interface with a dose of 2 x 10(16) cm(-2) at an energy of 18 keV, followed by an annealing step at 850degrees C for 600 s. MBE growth of an additional Si0.7Ge0.3 layer with a modulation doped strained Si QW on top results in a degree of relaxation of about 75%. At room temperature, a mobility of 1415 cm(2)/Vs has been measured. A cut-off frequency f(max)(MSG/MAG) = 95 GHz was achieved with RF devices having a gate length of 100 nm. Reference structures with several mum thick graded buffers resulted in an only marginally higher mobility of 1470 cm(2)/Vs and f(max) of 100 GHz. (C) 2003 Elsevier Science Ltd. All rights reserved.