InAs/AlSb HEMTs for Cryogenic Low-Noise Applications

Sammanfattning: The InAs/AlSb high electron mobility transistor (HEMT) is an emerging microwave device technology. The high electron mobility and high peak electron velocity of the InAs channel makes this device technology a potential candidate for low-noise applications operating at very low power dissipation. Until now the feasibility of InAs/AlSb HEMTs has been demonstrated at room temperature. Cryogenic operations are important in scientific instrumentation where lowest noise figure and highest gain are essential. However, cryogenic properties of the InAs/AlSb HEMT have not been reported so far. In this thesis, the design, the fabrication and the electrical characterization at room and cryogenic temperatures of the InAs/AlSb HEMT are presented. The device stability against oxidation has been improved using a new layout and passivation method. Furthermore, the InAs/AlSb HEMT gate scalability to 80nm has been demonstrated. The device properties of 110nm gate-length InAs/AlSb HEMTs have been investigated at low power levels (up to 70mW/mm). The DC, RF and noise performances have been measured at 300 K, 77K and 6K showing significant improvements for all the important device parameters. The DC measurements demonstrated significantly lower on-resistance, lower gate current leakage, and improved saturation behaviour of the drain current when the device was cooled down. Furthermore, an increase of more than 30% was observed in the peak transconductance at 6K for very low drain bias of 0.1 V. Large improvements when cooling down the InAs/AlSb HEMT have been measured for the RF and noise performances. The cut-off frequency and the maximum oscillation frequency increased 87% and 130%, respectively, at 6K and a drain bias of 0.1V whereas the minimum noise figure was reduced 68% at 77K for a frequency of 8 GHz. Anisotropic transport in the InAs channel of InAs/AlSb heterostructures grown on the InP substrate has been found and investigated. Significant differences in sheet resistance and channel electron mobility along different orientations were measured. As a result, InAs/AlSb HEMTs varied in drain current and peak transconductance around 25% depending upon device orientation.