G.S. Samudra

Solar Energy Research Institute of Singapore, Tumasik, Singapore

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Publications (211)295.39 Total impact

  • The 11th IEEE International Conference on Power Electronics and Drive Systems (PEDS), Sydney, Australia; 06/2015
  • International Conference on Compound Semiconductor Manufacturing Technology (CS MANTECH); 05/2015
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    ABSTRACT: In this letter, the approach of partial AlGaN recess and multiple layers of fluorinated Al2O3 gate dielectric is utilized to achieve highest reported positive gate threshold voltage ( $V_{{{textrm {TH}}}}$ ) without severe reduction on 2-D electron gas carrier mobility in AlGaN/GaN HEMTs. Guided by the design and verification through analytical model, proper fluorine ions incorporation is made through fabrication. The approach resulted in a high $V_{{{textrm {TH}}}}$ of +6.5 V and competitive drain saturation current ( $I_{{{textrm {DMAX}}}}$ ) of 340 mA/mm. Furthermore, low gate leakage current and high breakdown voltage of 1140 V were also demonstrated.
    IEEE Electron Device Letters 01/2015; 36(4):1-1. DOI:10.1109/LED.2015.2401736 · 3.02 Impact Factor
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    ABSTRACT: In this paper, an observation of drain current instability on p-GaN gate AlGaN/GaN HEMTs is reported. Contrary to the Schottky gate AlGaN/GaN HEMTs, which show stable and consistent Id-Vd curves under different pulsed conditions, the Id-Vd curves for p-GaN gate AlGaN/GaN HEMTs show a dispersion in the saturation region under the same pulse conditions, which cannot be explained by the trapping of electrons in the material. A model considering the trapping of holes in the p-GaN gate under different gate and drain biases is proposed to explain this new phenomenon.
    IEEE Transactions on Electron Devices 01/2015; 62(2):339-345. DOI:10.1109/TED.2014.2352276 · 2.36 Impact Factor
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    ABSTRACT: Multidimensional numerical simulation of boron diffusion is of great relevance for the improvement of industrial n-type crystalline silicon wafer solar cells. However, surface passivation of boron diffused area is typically studied in one dimension on planar lifetime samples. This approach neglects the effects of the solar cell pyramidal texture on the boron doping process and resulting doping profile. In this work, we present a theoretical study using a two-dimensional surface morphology for pyramidally textured samples. The boron diffusivity and segregation coefficient between oxide and silicon in simulation are determined by reproducing measured one-dimensional boron depth profiles prepared using different boron diffusion recipes on planar samples. The established parameters are subsequently used to simulate the boron diffusion process on textured samples. The simulated junction depth is found to agree quantitatively well with electron beam induced current measurements. Finally, chemical passivation on planar and textured samples is compared in device simulation. Particularly, a two-dimensional approach is adopted for textured samples to evaluate chemical passivation. The intrinsic emitter saturation current density, which is only related to Auger and radiative recombination, is also simulated for both planar and textured samples. The differences between planar and textured samples are discussed.
    Journal of Applied Physics 11/2014; 116(18):184103. DOI:10.1063/1.4901242 · 2.19 Impact Factor
  • International Conference on Solid State Devices and Materials (SSDM), Tsukuba, Japan; 09/2014
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    ABSTRACT: Effective minority carrier lifetime reduction at low injection levels is observed on 125 mm undiffused lifetime samples whose surfaces are under inversion due to field-effect passivation. With numerical analysis, we show that edge recombination is insufficient to account for this phenomenon on these samples. Between surface damage and asymmetric bulk lifetimes mechanisms that can account for the reduction, surface damage is confirmed to be more plausible. We demonstrate that the measured effective lifetime curves can be well reproduced assuming surface damage, a 700 nm thin layer with much lower bulk lifetimes, with numerical simulation.
    the 40th IEEE Photovoltaic Specialist Conference, Denver, CO, USA; 06/2014
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    ABSTRACT: During off-state, the influence of surface-trapped electron charges induced by high-field stress near the gate electrode of AlGaN/GaN power high-electron mobility transistor devices causes a reduction in two-dimensional electron gas (2DEG) carrier density at the heterointerface. In a pulse turn-on operation, the weakened 2DEG channel results in a higher on-state conduction resistance during the transient, known as the current collapse phenomenon. The phenomenon increases the switching loss by a higher on-state resistance and prolonged turn-on transition time, thus limits the device operating frequency range. In this paper, such a phenomenon is modeled, analyzed by Sentaurus TCAD simulation, and verified by the laboratory measurement data, with the emphasis on the influence of field plates toward the current collapse. The spatial distributions of trapped electrons and excess free electrons along the AlGaN surface are modeled and analyzed to arrive at the quantitative relationships among the trapped electron density, on-resistance increase, and the electric field distribution which provide a reliable criterion for current collapse reduction. It was found that, with a proper field plate design, it is possible to achieve an improvement on transient on-state resistance and the current recovery time.
    IEEE Transactions on Power Electronics 05/2014; 29(5):2164-2173. DOI:10.1109/TPEL.2013.2288644 · 5.73 Impact Factor
  • H. Huang, Y.C. Liang, G.S. Samudra, C.L.L. Ngo
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    ABSTRACT: In this letter, partially recessed gate structures in conjunction with negative trap charges by ${rm F}^{-}$ plasma treatments both at AlGaN barrier and on gate dielectric surface are employed to realize the normally-OFF operation for AlGaN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors in Au-free scheme. A partial gate recessed trench is designed to effectively reduce the 2-D electron gas (2DEG) density and achieve positive threshold voltage $({rm V}_{{rm th}})$ without severe degradation in 2-DEG channel mobility. Furthermore, the fixed trap charges are innovatively placed at the gate AlGaN and ${rm Si}_{{rm 3}}{rm N}_{{rm 4}}$ layers by a two-stage ${rm F}^{{-}}$ plasma treatment to further increase the ${rm V}_{{rm th}}$ , without mobility degradation. A high ${rm V}_{{rm th}}$ of 1.9 V and a drain current ${sim}{rm 200}~{rm mA}/{rm mm}$ are achieved in the fabricated device, which also has a lower leakage current and the higher breakdown voltage of 580 V.
    IEEE Electron Device Letters 01/2014; 35(5):569-571. DOI:10.1109/LED.2014.2310851 · 3.02 Impact Factor
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    ABSTRACT: This paper reports extensive modelling and analysis of the temperature dependence on the device characteristics of the AlGaN/GaN high electron mobility transistors (HEMTs). A physics-based model is proposed in this study in order to correctly predict the gate flat-band Schottky barrier height, energy band Fermi-level (EC-EF) at the AlGaN/GaN interface, two-dimensional electron gas sheet density, gate threshold and (ID-VG) at sub-threshold voltages, and drain current-voltage (ID-VD) characteristics under various high-temperature conditions. The analytical results are then verified by comparing with the laboratory measurement as well as the numerical results obtained from the Sentaurus TCAD simulation. The proposed model is found to be useful for power electronic device designers on the prediction of the AlGaN/GaN HEMT device performance under high-temperature operation.
    Semiconductor Science and Technology 12/2013; 28(12):5010-. DOI:10.1088/0268-1242/28/12/125010 · 2.21 Impact Factor
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    ABSTRACT: Normally-off operation is strongly desired for safety and efficient power switching in order to make the HEMT devices compatible with the currently used Si based IGBT and MOSFET devices. Combination of partially gate recess etching and gate insulator interface or floating gate charges in MIS structures is proposed and demonstrated for the first time to realize the normally-off mode. Partially gate trench can effectively reduce 2DEG density and shift threshold voltage (Vth) to positive without severely degrading in 2DEG channel conductance, while gate insulator interface or floating gate charges can further increase Vth at a relatively low charge density and thus maintain normally-off mode at a much longer time. Sentaurus TCAD is used to systematically simulate and predict the characteristics of the proposed structures. A positive Vth of larger than 3 V is demonstrated by employment of gate recess with 5~10 nm barrier leftover in combination of gate dielectric charging with a low sheet density of ~1012 cm-2. The proposed structures are very promising in future power switching applications due to the large positive Vth and the low gate leakage current density by adjusting the gate insulator thickness.
    Power Electronics and Drive Systems (PEDS), 2013 IEEE 10th International Conference on; 01/2013
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    ABSTRACT: The AlGaN/GaN high electron mobility transistor (HEMT) has drawn great interest in high power and high frequency applications owing to its outstanding material advantages, such as large critical electric field, high electron saturation velocity and the ability to form the high-density two dimensional electron gas (2DEG) conduction channel at the hetero interface. In this paper, a topical review on the device features is made, namely on its polarisation effects that lead to 2DEG formation at the AlGaN/GaN heterojunction, the surface field plate influence and the trap charges induced current collapse phenomenon during pulse operations. These effects are very important in understanding the AlGaN/GaN power HEMT devices.
    Next-Generation Electronics (ISNE), 2013 IEEE International Symposium on; 01/2013
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    ABSTRACT: Extraction of the exact surface recombination velocity at highly doped crystalline silicon (c-Si) surfaces is not straightforward and typically involves advanced computer modelling. In this work, two theoretical methods (the Kane-Swanson slope method and the general definition) for the extraction of the emitter saturation current density J0e are compared in SENTAURUS TCAD. We find good agreement between the J0e values obtained by the two methods. Experimental p+ emitter doping profiles on planar {100} samples are used to calibrate the process simulation, followed by a calculation of the doping profiles for textured {111} samples featuring upright pyramids. The experimentally measured J0e values of both textured and planar samples passivated by PECVD AlOx/SiNx stacks are reproduced by adjusting the surface recombination velocity. The electron surface recombination velocity parameter Sn0 at the p+ c-Si/AlOx interface is determined to be ∼1x104 cm/s for all investigated p+ emitters on planar wafers, comparable to values reported for lightly doped c-Si. A high density of fixed charge is found to reduce J0e by up to 90%, due to the suppression of Shockley-Read-Hall recombination at the surface.
    Energy Procedia 01/2013; 33:104–109. DOI:10.1016/j.egypro.2013.05.046
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    ABSTRACT: This paper reports analytical modelling and analysis of the temperature dependence on the device characteristics of the AlGaN/GaN high electron mobility transistors (HEMTs). A physics-based model is proposed in this study in order to correctly predict the gate Schottky barrier height (ΦB), Fermi-level from conduction band energy (EC-EF), two-dimensional electron gas (2DEG) sheet density, gate threshold (Vth) and sub-threshold voltages (ID-VG), and drain current-voltage (ID-VD) characteristics under various high temperature (300K~500K) conditions. The analytical results are then verified by comparing with the laboratory measurement as well as the numerical results obtained from the Sentaurus TCAD simulation. The proposed model is found to be useful for power electronic device designers on the prediction of the AlGaN/GaN HEMT device performance under high temperature operation without the use of heavy numerical solving process that requires complicated customized computer coding.
    ECCE Asia Downunder (ECCE Asia), 2013 IEEE; 01/2013
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    ABSTRACT: The slow recovery in pulsed drain current in AlGaN/GaN power HEMTs caused by high voltage stress during off-state becomes an important research topic in power electronic switching applications. To further investigate this phenomenon, the influence of gate drive towards the drain current recovery is investigated in this paper. The gate drive current can influence the de-trapping process along the AlGaN device surface, which then in turn affecting the 2DEG conductivity for the on-state current recovery. The analysis is made through the physical model and 2D T-CAD Sentaurus simulations, and verified by the experimental measurement. The proposed work is able to assist engineers in gate drive design for AlGaN/GaN power HEMT devices for fast pulsed current recovery in high-frequency switching.
    Power Electronics and Drive Systems (PEDS), 2013 IEEE 10th International Conference on; 01/2013
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    ABSTRACT: This paper reports the studies of the temperature dependence on the current collapse behaviours of AlGaN/GaN high electron mobility transistors (HEMTs). A physical-based model is proposed to analyse the trapping and de-trapping process along the surface with the effect of temperature included for the first time. The temperature-dependent gate leakage current is treated as the source for electron trapping and it can be predicted by the proposed model quantitatively. Then the relationship of the capture cross section of the surface trap on the electric field is investigated with respect to temperature variations. By applying the Poole-Frenkel emission mechanism, the dynamics of the trapped electrons at different temperatures are described in this model. The analytical results on current recovery time-constant are then verified by comparing with the laboratory measurement as well as the numerical results obtained from Sentaurus TCAD simulations.
    Wide Bandgap Power Devices and Applications (WiPDA), 2013 IEEE Workshop on; 01/2013
  • Shao-Ming Koh, Ganesh S. Samudra, Yee-Chia Yeo
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    ABSTRACT: In this work, strained n-channel FinFETs (nFinFETs) with silicon–carbon (Si:C) source/drain (S/D) stressors featuring NiSi:C contacts with segregated sulfur at the NiSi:C/Si:C interface are investigated in detail. The physical mechanism for the reduction in an effective Schottky barrier for electrons $\Phi_{B}^{n}$ due to presilicide sulfur ion implant and segregation is examined. The presence of sulfur near the NiSi:C/Si:C interface and its behavior as charged donor-like trap states was used to explain the enhancement of electron tunneling across the contact and the reduction in $\Phi_{B}^{n}$ down to 110 meV. New analysis using numerical simulation is presented. The results indicate that the presence of charged states near the interface plays a role in achieving low $\Phi_{B}^{n}$. When the S-segregated NiSi:C contact was integrated in strained nFinFETs with Si:C S/D stressors, external series resistance is reduced, and the drive current is improved. The dependence of the drive current on fin width and gate length is also studied.
    IEEE Transactions on Electron Devices 04/2012; 59(4):1046-1055. DOI:10.1109/TED.2012.2185799 · 2.36 Impact Factor
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    Fa-Jun Ma, Bram Hoex, Ganesh S. Samudra, Armin G. Aberle
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    ABSTRACT: An effective surface passivation plays a vital role in the performance of crystalline silicon (c-Si) solar cells. Experimental research shows that fixed charge-induced field-effect passivates the c-Si efficiently. In this work, n-type and p-type c-Si wafers symmetrically passivated by the negative-charge dielectric Al2O3 were numerically modelled with SENTAURUS TCAD. Surface recombination is traditionally modelled by employing the extended Shockley-Read-Hall (SRH) model with single energy level of interface traps. However, experiments show interface traps distribute across the silicon bandgap. Thus, we implemented the extended SRH model with the ability to describe arbitrary energy distribution of interface traps within the bandgap. The extended SRH model predicts a constant effective surface recombination velocity at low injection levels for lightly doped n-type and p-type c-Si passivated by dielectrics with either a high negative or positive charge density. However, this prediction contradicts experimental results which show a significant reduction of the effective lifetime at low injection levels if the polarity of the fixed charge is attracting the minority bulk charge carriers. One explanation is assuming the presence of a thin defect-rich layer close to the c-Si surface in which the lifetimes are degraded. However, the choice of the lifetime and depth of such damaged surface region seem rather arbitrary and its physical origin is still unclear. We show that unequal electron and hole bulk lifetime parameters can also account for the phenomenon. This proposition is physically plausible and the simulation results also show a good agreement with the experimental data from both n-type and p-type c-Si wafers passivated by Al2O3. Our modelling results predict a simple but unambiguous experiment to distinguish between these two explanations.
    Energy Procedia 01/2012; 15:155–161. DOI:10.1016/j.egypro.2012.02.018
  • Huolin Huang, Y.C. Liang, G.S. Samudra
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    ABSTRACT: In this paper, the influences of Al mole fraction and AlGaN layer strain relaxation on the bound polarization charges and the 2DEG concentration are investigated by theoretical calculation. The calculated sheet polarization charge data is used to preset Sentaurus TCAD to simulate the performance characteristics of the GaN HEMT device. The proposed method is proven to be a simple, equally accurate and effective approach in the simulations. For simplicity and time-saving, the theory-based hybrid method can be employed extensively in the simulations of GaN heterostructures power devices.
    Electron Devices and Solid State Circuit (EDSSC), 2012 IEEE International Conference on; 01/2012
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    ABSTRACT: Tellurium (Te) implantation was introduced to tune the effective electron Schottky barrier height (SBH) Φ<sub>B</sub><sup>n</sup> of platinum-based silicide (PtSi) contacts formed on n-type silicon-carbon (Si:C). Te introduced by ion implantation prior to Pt deposition segregated at the PtSi:C/Si:C interface during PtSi:C formation. The presence of Te at the PtSi:C/Si:C interface leads to a low Φ<sub>B</sub><sup>n</sup> of 120 meV for PtSi:C contacts. The integration of Te-segregated PtSi:C contacts on strained n-channel fin field-effect transistors (FinFETs) with Si:C source/drain (S/D) stressors achieves the lowering of the parasitic series resistance R <sub>SD</sub> by ~62% and increases the saturation drive current by ~22%. The Te-segregated contact-resistance reduction technology does not degrade the short-channel effects and positive-bias temperature instability characteristics of n-FinFETs with Si:C S/D. As PtSi has a low SBH for holes and is a suitable contact for p-FinFETs, this new contact-resistance reduction technology has potential to be introduced as a single-metal-silicide dual-barrier-height solution for future complementary metal-oxide-semiconductor FinFET technology.
    IEEE Transactions on Electron Devices 12/2011; 58(11-58):3852 - 3862. DOI:10.1109/TED.2011.2166077 · 2.36 Impact Factor

Publication Stats

2k Citations
295.39 Total Impact Points

Institutions

  • 2012–2013
    • Solar Energy Research Institute of Singapore
      Tumasik, Singapore
  • 1999–2013
    • National University of Singapore
      • • Department of Electrical & Computer Engineering
      • • Faculty of Engineering
      Tumasik, Singapore
  • 2007
    • Nanyang Technological University
      Tumasik, Singapore