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1. Role of transverse effective mass in Auger generation impacted planar III-V Tunnel FETs

   https://doi.org/10.1109/DRC46940.2019.9046439  

   Ahmed, Sheikh Z. ; Tan, Yaohua ; Ghosh, Avik W. ( June 2019 , 2019 Device Research Conference (DRC))

   null (Ed.)

   The Tunnel field-effect-transistor (TFET) has widely been considered as one of the most viable replacements to the complementary metal oxide semiconductor (CMOS) devices due to their superior theoretical performance. Practically, though there have been scant demonstrations of the sub-60mV/dec of TFETs 1 , it has yet to be realized at acceptable current levels over a substantial current swing needed for circuit operation. It is therefore imperative to study the primary delimiters of TFETs, mainly trap-assisted tunneling (TAT) and Auger generation 2-4 , along with ways to reduce them in order to improve device performance. The effect of TAT in TFETs has been studied extensively 3,4 . Here, we study the role of transverse effective mass on Auger generation in a planar TFET and propose a method of improving device performance. 

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2. Auger effect limited performance in tunnel field effect transistors

   https://doi.org/10.1109/E3S.2017.8246156  

   Ahmed, Sheikh ; Tan, Yaohua ; Truesdell, Daniel ; Ghosh, Avik ( October 2017 , 2017 Fifth Berkeley Symposium on Energy Efficient Electronic Systems & Steep Transistors Workshop (E3S))

   null (Ed.)

   Tunnel field-effect-transistors (TFETs) are promising candidates for next generation transistors for low power applications, as the TFETs promise low subthreshold swing (SS). Different from traditional MOSFET, the TFETs rely on energy-efficient switching of band-to-band tunneling (BTBT), therefore the SS in TFETs is not limited by the 60 mV/decade Boltzmann limit. This reduction in energy consumption makes TFETs suitable candidates to replace standard MOSFETs in low power applications. However, most experimentally demonstrated TFETs suffer from low on current[1], and the theoretical low SS is compromised by impurities and Auger generation. To understand the underlying physics and predict the device characteristics of TFETs, sophisticated numerical simulations can be used. On the other hand, physics based compact models are also required to provide fast predictions for existing and new device concepts. Furthermore, a physics based compact model is more efficient to model the effects like Auger generation which could be time-consuming for numerical calculations. In this work, we introduce a physics based compact model for homojunction TFETs with Auger generation effect considered. This compact model is based on the modified Simmons' equation at finite temperature[2]. With our compact model, the possible impact of Auger generation effect to off-current and SS is explored. 

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3. InP MOSFETs Exhibiting Record 70 mV/dec Subthreshold Swing

   Tseng, Hsin-Ying ; Fang, Yihao ; Zhong, Shibo ; Rodwell, Mark ( June 2019 , 2019 IEEE Device Research Conference)

   Low InP/dielectric interface trap density Dit will enable low subthreshold swings (SS) in mm-wave MOSFETs [1] using InGaAs/InP composite channels [2] for increased breakdown and in tunnel FETs (TFETs) [3] using InAs/InP heterojunctions [4] for increased tunneling probability. Reducing Dit at the etched InP mesa edges of DHBTs and avalanche photodiodes will reduce leakage currents and increase breakdown voltages. While it can be difficult [5] to extract Dit of III-V interfaces from MOSCAP characteristics, Dit can be readily determined from the SS of long gate length Lg MOSFETs. Here we report InP-channel MOSFETs with record low SS indicating record low Dit at the semiconductor-dielectric interface. The devices use a AlOxNy/ZrO2 gate dielectric and a 14nm channel thickness Tch. A sample of 13 MOSFETs at 2 m Lg shows SS=70mV/dec. (mean) ±3 mV/dec. (standard deviation), corresponding to a minimum Dit ~3×1012 cm-2eV-1. The lowest SS observed at 2 m Lg is 66 mV/dec. The results suggest that wide-bandgap InP layers can be incorporated into MOS device designs without large degradations in DC characteristics arising from interface defects 

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4. Surface passivation extends single and biexciton lifetimes of InP quantum dots

   https://doi.org/10.1039/D0SC01039A  

   Yang, Wenxing ; Yang, Yawei ; Kaledin, Alexey L. ; He, Sheng ; Jin, Tao ; McBride, James R. ; Lian, Tianquan ( June 2020 , Chemical Science)

   Indium phosphide quantum dots (InP QDs) are nontoxic nanomaterials with potential applications in photocatalytic and optoelectronic fields. Post-synthetic treatments of InP QDs are known to be essential for improving their photoluminescence quantum efficiencies (PLQEs) and device performances, but the mechanisms remain poorly understood. Herein, by applying ultrafast transient absorption and photoluminescence spectroscopies, we systematically investigate the dynamics of photogenerated carriers in InP QDs and how they are affected by two common passivation methods: HF treatment and the growth of a heterostructure shell (ZnS in this study). The HF treatment is found to improve the PLQE up to 16–20% by removing an intrinsic fast hole trapping channel ( τ h,non = 3.4 ± 1 ns) in the untreated InP QDs while having little effect on the band-edge electron decay dynamics ( τ e = 26–32 ns). The growth of the ZnS shell, on the other hand, is shown to improve the PLQE up to 35–40% by passivating both electron and hole traps in InP QDs, resulting in both a long-lived band-edge electron ( τ e > 120 ns) and slower hole trapping lifetime ( τ h,non > 45 ns). Furthermore, both the untreated and the HF-treated InP QDs have short biexciton lifetimes ( τ xx ∼ 1.2 ± 0.2 ps). The growth of an ultra-thin ZnS shell (∼0.2 nm), on the other hand, can significantly extend the biexciton lifetime of InP QDs to 20 ± 2 ps, making it a passivation scheme that can improve both the single and multiple exciton lifetimes. Based on these results, we discuss the possible trap-assisted Auger processes in InP QDs, highlighting the particular importance of trap passivation for reducing the Auger recombination loss in InP QDs. 

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5. Towards Horizontal Heterojunctions for Tunnel Field Effect Transistors with Template Assisted Selective Epitaxy via MOCVD

   Brunelli, S ; Wu, J ; Tseng, HS ; Rodwell, M ; Palmstrom, C ; Klamikin, J. ( June 2018 , International conference on OMVPE, 2018)

   A unique confined lateral selective epitaxial growth (CLSEG) [1] technique for next generation semiconductor devices was demonstrated in [2, 3] and termed template assisted selective epitaxy (TASE). This technique is based on the formation of hollow confined structures that drive subsequent growth initiation only from a small area of the substrate exposed to the growth environment, dubbed a seed, and continued growth is forced within the template. This allows to arbitrarily determine the shape and orientation of the grown material and to form novel nano-electronic device structures. Here, results are reported on the fabrication of channel-like nanometer sized horizontal structures, and, the subsequent homoepitaxy of indium phosphide (InP) to demonstrate the potential for TASE to create vertical heterojunctions that could enable the next generation of tunnel field-effect transistors (TFETs) [4]. Templates were fabricated with a combination of e-beam lithography, PECVD deposition, resist patterning, and selective wet etches, on (100) n-type InP wafers. Homoepitaxy was done via MOVPE achieving growth selectivity with a growth temperature of 640°C, group III precursor molar rate of 4E-6 mol/min, a V/III ratio of 400. Trimethylindium (TMIn) and tertiarybutylphosphine (TBP) are used as indium and phosphorus precursors respectively. Characterization via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was employed to determine the success of growth in the template, initiation at the “seed”, area selectivity, faceting at the growth front, and conformality to the template. Each die consisted in a parametric array of structures of varying characteristic sizes that allows, via growth-interrupt trials, to analyze confined growth behavior and how this deviates from bulk epitaxy. Initial data suggests growth rate suppression with increased channel length. MOVPE in these conditions is known to be mass transport limited [5], so this could be explained with the need for the precursors to diffusively cover longer distances. 

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