Optical spin orientation and depolarization in Ge

TL;DR

This study investigates optical spin orientation and depolarization in germanium using spin-photodiodes, revealing spectral dependence, a second peak at 530 nm, and short hole spin lifetimes with implications for spin diffusion.

Contribution

It provides the first detailed spectral analysis of spin polarization in Ge across 400-1550 nm and identifies a second peak related to L valley photo-generation.

Findings

Maximum spin polarization at 1550 nm corresponding to direct gap

A second peak at 530 nm due to L valley photo-generation

Hole spin lifetime estimated at 5-10 ps with diffusion length 150-220 nm

Abstract

Optical spin orientation and depolarization phenomena in semiconductors are of overwhelming importance for the development of spin-optoelectronics. In this paper we employ Ge-based spin-photodiodes to investigate the room temperature spectral dependence of optical spin orientation in Germanium, in the range 400-1550 nm, and the photo-carrier spin relaxation phenomena. Apart from the maximum in the spin polarization of photo-carriers for photon energy resonant with the direct gap (1550 nm), we experimentally demonstrate the presence of a second sizable peak at 530 nm due to photo-generation far away from the center of the Brillouin zone, within the L valleys. Furthermore, our data indicate that the equivalent the spin lifetime of holes in Ge is in the order of 5-10 ps, meaning that the spin diffusion length for holes at room temperature is larger than expected, in the order of 150-220 nm.