Surface Passivation Technique for Ge_1–xSn_x-Based Diodes by GeO₂ Atomic Layer Deposition with Postoxidation Annealing

High Resolution Image Download MS PowerPoint Slide Ge 1– x Sn x /Ge 1– x – y Si x Sn y heterostructures enable monolithic integration of photonics and electronics on Si ultralarge-scale integration. The development of the Ge 1– x Sn x /Ge 1– x – y Si x Sn y resonant tunneling diode (RTD) composed of group-IV semiconductors is crucial for their use as oscillators in terahertz (THz) communication systems. Surface passivation techniques are crucial in enhancing the performance of these devices. This study investigates the atomic layer deposition (ALD) of GeO 2 combined with postoxidation annealing (POA) for the surface passivation of Ge-based Group IV alloy semiconductor devices. Initially, we developed an ALD process for the deposition of GeO 2 using tetraethoxygermanium and ozone as precursors. We investigated the GeO 2 ALD condition, resulting in a growth rate of 0.35 Å/cycle at 200 °C. Subsequently, we demonstrated the effectiveness of the ALD-GeO 2 passivation in conjunction with POA by fabricating mesa-structured Ge 0.948 Sn 0.052 /Ge p–n diodes. The incorporation of an ALD-GeO 2 interlayer at the insulator/semiconductor interface and POA proved to be effective in suppressing the surface leakage current in Ge 1– x Sn x -based diodes. Furthermore, we fabricated Al/ALD-GeO 2 /p-Ge and Al/ALD-Al 2 O 3 /p-Ge metal-oxide-semiconductor capacitors (MOSCAPs) to clarify the mechanism of the reverse current reduction by introducing an ALD-GeO 2 layer and POA. ALD-GeO 2 MOSCAPs demonstrated a lower interface state density compared with ALD-Al 2 O 3 MOSCAPs, along with a negative bias shift in the flat-band voltage by POA. The suppression of surface leakage current through the combined use of ALD-GeO 2 and POA can be attributed to both chemical and field-effect passivation concepts. An ALD-GeO 2 layer with POA is poised to become a key passivation technique for both Ge 1– x Sn x /Ge 1– x – y Si x Sn y p-RTD and versatile Ge-based Group IV alloy semiconductor devices.