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Sukhdeo, David S.,Gupta, Shashank,Saraswat, Krishna C.,Dutt, Birendra (Raj),Nam, Donguk IOP Publishing 2016 Japanese journal of applied physics Vol.55 No.2
<P>We theoretically investigate the methodology involved in the minimization of the threshold of a Ge-on-Si laser and maximization of the slope efficiency in the presence of both biaxial tensile strain and n-type doping. Our findings suggest that there exist ultimate limits beyond which no further benefit can be realized through increased tensile strain or n-type doping. In this study, we quantify these limits, showing that the optimal design for minimizing threshold involves approximately 3.7% biaxial tensile strain and 2 x 10(18)cm(-3) n-type doping, whereas the optimal design for maximum slope efficiency involves approximately 2.3% biaxial tensile strain with 1 x 10(19)cm(-3) n-type doping. Increasing the strain and doping beyond these limits will degrade the threshold and slope efficiency, respectively. (C) 2016 The Japan Society of Applied Physics</P>
Sukhdeo, David,Kim, Yeji,Gupta, Shashank,Saraswat, Krishna,Dutt, Birendra,Nam, Donguk IEEE 2016 IEEE electron device letters Vol.37 No.10
<P>We investigate the interaction of tin alloying with tensile strain and n-type doping for improving the performance of a Ge-based laser for on-chip optical interconnects. Using a modified tight-binding formalism that incorporates the effect of tin alloying on conduction band changes, we calculate how threshold current density and slope efficiency are affected by tin alloying in the presence of tensile strain and n-type doping. Our results show that while there exists a negative interaction between tin alloying and n-type doping, tensile strain can be effectively combined with tin alloying to dramatically improve the Ge gain medium in terms of both reducing the threshold and increasing the expected slope efficiency. Through quantitative modeling, we find that the best design is to include large amounts of both tin alloying and tensile strain but only moderate amounts of n-type doping, if researchers seek to achieve the best possible performance in a Ge-based laser.</P>
Sukhdeo, David S,Nam, Donguk,Kang, Ju-Hyung,Brongersma, Mark L,Saraswat, Krishna C Optical Society of America 2015 Optics express Vol.23 No.13
<P>Strain engineering has proven to be vital for germanium-based photonics, in particular light emission. However, applying a large permanent biaxial tensile strain to germanium has been a challenge. We present a simple, CMOS-compatible technique to conveniently induce a large, spatially homogenous strain in circular structures patterned within germanium nanomembranes. Our technique works by concentrating and amplifying a pre-existing small strain into a circular region. Biaxial tensile strains as large as 1.11% are observed by Raman spectroscopy and are further confirmed by photoluminescence measurements, which show enhanced and redshifted light emission from the strained germanium. Our technique allows the amount of biaxial strain to be customized lithographically, allowing the bandgaps of different germanium structures to be independently customized in a single mask process.</P>
Petykiewicz, Jan,Nam, Donguk,Sukhdeo, David S.,Gupta, Shashank,Buckley, Sonia,Piggott, Alexander Y.,Vuč,ković,, Jelena,Saraswat, Krishna C. American Chemical Society 2016 NANO LETTERS Vol.16 No.4
<P>A silicon-compatible light source is the final missing piece for completing high-speed, low-power on-chip optical interconnects. In this paper, we present a germanium nanowire light emitter that encompasses all the aspects of potential low-threshold lasers: highly strained germanium gain medium, strain-induced pseudoheterostructure, and high-Q nanophotonic cavity. Our nanowire structure presents greatly enhanced photoluminescence into cavity modes with measured quality factors of up to 2000. By varying the dimensions of the germanium nanowire, we tune the emission wavelength over more than 400 nm with a single lithography step. We find reduced optical loss in optical cavities formed with germanium under high (>2.3%) tensile strain. Our compact, high-strain cavities open up new possibilities for low-threshold germanium based lasers for on-chip optical interconnects.</P>