Room-temperature efficient light detection by amorphous Ge quantum wells

Salvatore Cosentino,Antonio Terrasi,Salvatore Mirabella,Maria Miritello,Francesca Simone,Corrado Spinella,Isodiana Crupi,Giuseppe Nicotra

doi:10.1186/1556-276x-8-128

Salvatore Cosentino, Antonio Terrasi + Show 6 more

Open Access

https://doi.org/10.1186/1556-276x-8-128

Copy DOI

Abstract

In this work, ultrathin amorphous Ge films (2 to 30 nm in thickness) embedded in SiO2 layers were grown by magnetron sputtering and employed as proficient light sensitizer in photodetector devices. A noteworthy modification of the visible photon absorption is evidenced due to quantum confinement effects which cause both a blueshift (from 0.8 to 1.8 eV) in the bandgap and an enhancement (up to three times) in the optical oscillator strength of confined carriers. The reported quantum confinement effects have been exploited to enhance light detection by Ge quantum wells, as demonstrated by photodetectors with an internal quantum efficiency of 70%.

Highlights

Due to its large compatibility with Si technology and to its pseudodirect bandgap, germanium has recently drawn a vast scientific concern for promising electronic and photonic applications [1,2,3,4,5]
We report on the large bandgap tuning observed at room temperature in amorphous Ge quantum wells (QWs) (2 to 30 nm in thickness) due to quantum confinements effects
If relevant fractures occurred in the Ge film, the quantum confinement would change from one-dimensional (1D) regime to two-dimensional (2D) or three-dimensional (3D) regimes, as the unconfined feature of the electron wave functions in the plane parallel to the surface would be lost

Summary

Introduction

Due to its large compatibility with Si technology and to its pseudodirect bandgap, germanium has recently drawn a vast scientific concern for promising electronic and photonic applications [1,2,3,4,5]. Quantum confinement [1,6] and tensile strain [2,3,4] effectively modify the electronic bandgap of crystalline (c-) Ge, in such a way that it opens the route for Si-compatible, room-temperature operable devices as optical modulators [1,2] or lasers in the commercial C-band [4]. Photoluminescence peak coming from excitons confinÀed inÁ Ge nanocrystals exceeds the bandgap of Ge bulk EGbulk by an energy amount much larger than that for Si nanocrystals [9]. Still, all these effects have been extensively proven for c-Ge NS, while the light interaction with amorphous (a-) NS of Ge was poorly investigated. Fabrication of amorphous materials is typically less expensive than that of crystalline materials due to lower synthesis temperatures, higher deposition

Methods

Results

Conclusion