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The noise spectrum in micro-Hall devices based on pseudomorphic Al0.2Ga0.8As/In0.1Ga0.9As/GaAs modulation-doped heterostructures was measured between 4 Hz and 65 kHz, allowing components due to thermal, 1/f, and generation-recombination to be characterized. Applying deep level noise spectroscopy (DLNS) in the temperature range of 77-300 K to analyze the generation-recombination part of the spectrum, two electron traps contributing to noise density were identified. An emission activation energy of 474 meV was measured for the dominant trap, corresponding to the well-known DX center originating from the AlGaAs barrier. The other deep level, with an emission activation energy of 242 meV, is probably related to defects in the InGaAs layer. The structures under investigation resulted in high-performance micro-Hall devices: a supply-current-related sensitivity up to 725 V·A-1·T-1 at 77 K independent of bias current, a signal-to-noise sensitivity of 155 dB·T-1 and a detection limit of 340 pT·mm·Hz-12/ at 77 K were measured.