We have examined type II band alignment in Ge1-x-ySixSny/Ge1-α-βSiαSβ heterojunctions grown on virtual substrates in Si platform. It is found that, for different values of x, y, α and β direct band gap type II band line up can be achieved for both tensile and compressive strains. The calculated band gap energy corresponds to the mid infrared to far infrared regions in the electromagnetic spectrum. © 2017 Elsevier Ltd

BRATATI MUKHOPADHYAY

Radio Physics and Electronics

S DEY

G SEN

P K BASU

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Solid State Communications

This paper aims to provide the performance characteristics of proposed, strain balanced direct band gap multiple quantum wells (MQWs) hetero phototransistor (HPT) made of SiGeSn/GeSn alloys grown on Si substrate which is compatible with recent CMOS fabrication technology. This also presents a comprehensive comparison of this proposed structure with the existing HPT structure made of indirect gap Ge/SiGe MQWs. Alloys of Ge and Sn grown on Si platform shows about tenfold increase in absorption over Ge at C and L-bands due to direct nature of band gap in GeSn. Initial work begins the solution of continuity equation to solve the different terminal current densities and optical gain of the multiple quantum well structure. Main analysis was concentrated on finding the external quantum efficiency depending on the doping variations of emitter and base, base width etc. Finally the photocurrent density variations are estimated for the structure and compared with existing indirect band gap HPT. The calculated values for direct band gap GeSn HPT device are found to be comparable with those for indirect band gap SiGe device to flourish as a potential candidate of photo detectors for the present day telecommunication network. © 2017, Springer Science+Business Media New York.

Optical and Quantum Electronics

Current gain and external quantum efficiency modeling of GeSn based direct bandgap multiple quantum well heterojunction phototransistor

Group IV semiconductor-based alloy Ge1−xSnx can be grown on Si platform and a crossover from indirect (L valleys) to direct gap (Γ valley) occurs for x &gt; 0.08. The direct gap alloy shows promise for use in high-speed electronic and photonic devices. An earlier study predicted that the electron mobility in the alloy would increase by a few orders of magnitude above the value for pure Ge. In that work, however, electrons were assumed to occupy only the low effective mass Γ valley and only the deformation potential acoustic phonon and alloy scatterings were considered. In the present work, we give a more realistic estimate of the values of electron mobility in direct gap GeSn alloy, considering the Γ and L valleys and the phonon (deformation potential acoustic, optical and intervalley), alloy, and impurity scatterings. The effect of strain, both tensile and compressive, on the mobility is also studied. It is found that for higher alloy composition and suitable strain, mobility values ∼2 × 105 cm−2/V · s, more than 50 times higher than the value in pure Ge (3900 cm2/V · s) may be achieved. This is attributed to increased separation between Γ and L valleys and consequent reduction in intervalley scattering. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Physica Status Solidi (B) Basic Research

Prediction of Large Enhancement of Electron Mobility in Direct Gap Ge1âˆ’xSnx Alloy

We propose the use of Ge1-xSnx heterojunction phototransistors (HPTs) as efficient optical receivers on Si substrates and analyze their performance. Our designs use n-Ge/p-Ge1-x}Snx/n-Ge1-xSnx layers pseudomorphically grown on Si wafers via a Ge virtual substrate, which offers compatibility with complementary metal-oxide-semiconductor (CMOS) technology. By incorporating Sn into the Ge photon-absorbing layer to shrink the bandgap, the photodetection range can be significantly extended to the mid-infrared (MIR) region with a considerably enhanced optical response. The use of HPT structures provides optical conversion gain to further enhance the optical responsivity, thereby enabling efficient photodetection in the short-wave infrared region. We develop theoretical models to calculate the composition-dependent band alignments, the band structures (by taking into account the nonparabolic effect), the absorption coefficient, and the optical responsivity for the proposed GeSn HPTs. As the Sn content increases, the conduction band nonparabolicity becomes increasingly significant and considerably impacts the optical absorption coefficient. Moreover, analysis of the spectral response for the Ge1-x Snx HPTs shows that efficient photodetection covering the entirety of the fiber-optic telecommunication bands, as well as the emerging 2-μm MIR communication band, can be achieved. These results indicate that the proposed Ge1-x Snx HPTs are attractive for use as high-responsivity CMOS-compatible photodetectors in communication applications. © 1995-2012 IEEE.

IEEE Journal on Selected Topics in Quantum Electronics

Design and modeling of GeSn-based heterojunction phototransistors for communication applications

Alloys of Ge and Sn grown on Si platform show about tenfold increase in the absorption over Ge at C and L-bands due to the direct nature of the band gap in GeSn. This led us to propose a Ge/GeSn/GeSn heterophototransistor (HPT) structure on a Si-platform and to calculate the terminal currents, current gain, optical gain and responsivity of the device at (Formula presented.). The model developed by Frimel and Roenker for HPTs with InGaAs base is used. In the model, the carrier density in the base is obtained by matching the diffusion-limited current with the current due to thermionic emission and tunneling across the emitter-base heterobarrier, and also considering the carrier density at the collector-end limited by the saturation drift velocity. The contribution of holes to the current is also included. The resulting carrier distribution is used to express the terminal currents and calculate the values of gain. The band gap for GeSn and the band discontinuity in the heterobarrier are calculated by using model solid theory. The calculated values for the GeSn HPT are found to be comparable with and even better than the corresponding values for the InP/InGaAs/InGaAs Npn device for lower values of the base thickness and the base doping. © 2014, Springer Science+Business Media New York.

Journal	Data powered by TypesetSolid State Communications
Publisher	Data powered by TypesetElsevier Ltd
ISSN	0038-1098
Open Access	No