Highly sensitive nanohall sensors on GaAlAs/GaAs heterojunctions

We present an experimental study on the performance of nano-Hall sensors made on the two dimensional electron gaz of a pseudo morphic GaAlAs/GaInAs heterostructures. The active area of the sensor is from sub-micronic scale (down to 500 nm) to 5 microns. Ohmic contacts have micronic size, and a reference sample of 80 micron width has been caracterized as well, as a reference. In our process, we have improved the contacts technology to limit the thermal Shottky noise. Thus although ohmic contacts have small dimensions they have low resistance and do not limit the sensitivity of our nano-sensors. Extensive caracterization of those devices demonstrate a diffusive transport at 300 K, and a magnetic field sensitivity up to 1000 V/T/A. We have focused our attention on the smallest detectable magnetic field in the smallest sensor, and performed a systematic study of the noise measurements. We have measured the excess noise in both the longitudinal configuration and the Hall configuration, as a function of the current. Our noise measurements performed at room temperature in the range [1 Hz-100 kHz] show, at low frequency, an 1/f noise spectrum whose intensity is proportional to the square of the current. We understand our data by the conductivity fluctuations model and we obtain the Hooge parameter for this technology. We demonstrate that the noise intensity is inversely proportional to area of the sensor. Of course reducing the dimensions induces physical limitations but we demonstrate that a magnetic field of few μT can be measured with a micron scale sensor at low frequencies; at higher frequencies, when the thermal noise limits the resolution, the measurement of 300 nT is achievable.