# On the Angular Dependence of InP High Electron Mobility Transistors for Cryogenic Low Noise Amplifiers in a Magnetic Field

## TL;DR

This study investigates how the orientation of InP HEMTs affects their performance in cryogenic magnetic fields, revealing a strong angular dependence that impacts their use in sensitive microwave detection systems.

## Contribution

It demonstrates the angular dependence of InP HEMT performance in magnetic fields at cryogenic temperatures, highlighting the importance of device orientation for low noise amplifier applications.

## Key findings

- Significant gain and noise temperature degradation at 1.5T when perpendicular to magnetic field.
- Strong reduction in transistor output current up to 14T, dependent on orientation.
- Key parameters like transconductance and on-resistance are highly affected by magnetic field angle.

## Abstract

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. We observed that an InP HEMT 0.3-14GHz LNA at 2K, where the in-going transistors were oriented perpendicular to a magnetic field, heavily degraded in gain and average noise temperature already up to 1.5T. Dc measurements for InP HEMTs at 2K revealed a strong reduction in the transistor output current as a function of static magnetic field up to 14T. In contrast, the current reduction was insignificant when the InP HEMT was oriented parallel to the magnetic field. Given the transistor layout with large gate width/gate length ratio, the results suggest a strong geometrical magnetoresistance effect occurring in the InP HEMT. This was confirmed in the angular dependence of the transistor output current with respect to the magnetic field. Key device parameters such as transconductance and on-resistance were significantly affected at small angles and magnetic fields. The strong angular dependence of the InP HEMT output current in a magnetic field has important implications for the alignment of cryogenic LNAs in microwave detection experiments involving magnetic fields.