Cryogenic InP High Electron Mobility Transistors in a Magnetic Field
The InGaAs-InAlAs-InP high electron mobility transistor (InP HEMT) is the preferred active device used in a cryogenic low noise amplifier (LNA) for sensitive detection of microwave signals. In this thesis it is demonstrated that the InP HEMT, when placed in a magnetic field, has a strong angular dependence in its output current. This has important implications for the alignment of cryogenic InP HEMT LNAs in microwave detection experiments involving magnetic fields.
InP HEMTs with various gate lengths and gate widths have been fabricated and characterized. The output current for the InP HEMTs was measured in static magnetic fields up to 14 T at different angles in an ambient temperature of 2 K. The results showed that for all InP HEMT devices placed in a perpendicular arrangement, the output current is drastically suppressed. It is shown that the reduction in output current is negligible once placed parallel to the applied field. Furthermore, it was found that the output current strongly depends on the angle between the current direction and the magnetic field. In the investigated device geometry, the output current in the InP HEMT is limited by geometrical magnetoresistance. This was expressed in an output current equation which showed excellent agreement with measured data as a function of angle and magnetic field. Device parameters such as transconductance and on-resistance were found to be significantly affected even at small angles and magnetic fields.
A 0.3-14 GHz cryogenic LNA module based on the same transistor technology used in device experiments was measured in a perpendicular magnetic field at 2 K. The LNA was heavily degraded in gain and average noise temperature already up to 1.5 T. In comparison with previous work reported for GaAs single-heterojunction HEMT LNAs, it is shown here that the effect is much stronger for InP HEMT cryogenic LNAs.
low noise amplifier