Halsall is a senior PSI photonics researcher focusing on semiconductor spectroscopy and photonic quantum device characterization. Research directions: (1) Deep-level transient spectroscopy (DLTS) — characterizing defects and impurities in semiconductor quantum device structures (Si, GaN, SiC) that are relevant to qubit coherence; (2) Photoluminescence mapping — spatial mapping of optical quality in quantum well and dot wafers for quantum sensing device development; (3) InGaN/GaN quantum wells — non-destructive optical characterization of LED and sensor structures; (4) THz and infrared spectroscopy — contactless Hall measurements and Drude response for quantum material characterization. Provides photonic metrology tools for characterizing quantum sensing device materials.