Open AccessTensile-strained, n-type Ge as a gain medium for monolithic laser integration on Si
Author(s) -
Jifeng Liu,
Xiaochen Sun,
Dong Pan,
Xiaoxin Wang,
Lionel C. Kimerling,
Thomas Koch,
Jürgen Michel
Publication year - 2007
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.15.011272
Subject(s) - materials science , lasing threshold , doping , laser , ultimate tensile strength , band gap , optoelectronics , population inversion , direct and indirect band gaps , heterojunction , optics , composite material , physics , wavelength
We analyze the optical gain of tensile-strained, n-type Ge material for Si-compatible laser applications. The band structure of unstrained Ge exhibits indirect conduction band valleys (L) lower than the direct valley (Gamma) by 136 meV. Adequate strain and n-type doping engineering can effectively provide population inversion in the direct bandgap of Ge. The tensile strain decreases the difference between the L valleys and the Gamma valley, while the extrinsic electrons from n-type doping fill the L valleys to the level of the Gamma valley to compensate for the remaining energy difference. Our modeling shows that with a combination of 0.25% tensile strain and an extrinsic electron density of 7.6x10(19)/cm(3) by n-type doping, a net material gain of ~400 cm(-1) can be obtained from the direct gap transition of Ge despite of the free carrier absorption loss. The threshold current density for lasing is estimated to be ~6kA cm(-2) for a typical edgeemitting double heterojunction structure. These results indicate that tensile strained n-type Ge is a good candidate for Si integrated lasers.