UC Santa Cruz

Photodiodes are an essential semiconductor device used in medical imaging, high-energy physics, and UV-visible sensors. Recent progress has renewed interest in exploring alloys of traditional materials for detector fabrication. Alloying amorphous selenium (a-Se) with other materials can potentially improve device performance in responsivity and quantum conversion efficiency (QCE) and address some limitations of stabilized a-Se. To increase the sensitivity and transport properties, we explore multilayer devices with vertical and lateral architectures. We use different combinations of stabilized a-Se and selenium-tellurium (Se-Te) alloys and compare implementing each as the light-absorbing layer, aiming to determine whether tailoring the alloys based on the wavelength absorption depth could improve the detector’s performance. For vertical devices, a thin (90 nm) a-Se layer paired with a thick (15 μm) Se-Te layer proved to be the most effective device, improving both the response at long wavelengths and overall QCE, with a 13-15% improvement over single-layer a-Se devices in the UV and 2.5% improvement at red wavelengths. In the lateral devices, the combination of a-Se and Se-Te layers outperformed a single layer of stabilized a-Se; however, a solid layer of Se-Te gave the highest QCE with a peak efficiency of 30% at 355 nm and 15 V/μm. These findings demonstrate how multilayer structures can affect device performance, better guiding device architecture based on the end application, desired wavelength sensitivity, and efficiency.