Browsing by Author "Nagarajan, Venkatesan"

Now showing 1 - 7 of 7

A simple extraction method for parasitic series resistances in GaN HEMTs considering non-quasi-static effects
(2019-05-01)
Nagarajan, Venkatesan
;
Chen, Kun-Ming
;
Wang, Huan-Chung
;
Singh, Sankalp Kumar
;
Anandan, Deepak
A simple technique for extracting the bias-dependent parasitic series resistances of the GaN-based high electron mobility transistor (HEMT) is demonstrated in this paper. With considering the non-quasi-static effect in devices, new analytical Z-parameter formulations are derived to determine parasitic resistances using the curve-fitting algorithm. More accuracy parasitic resistances can be obtained over a wide fitting frequency range compared to the conventional method which ignores the non-quasi-static effect. Here the intrinsic parameters are then calculated directly from intrinsic Y-parameters after de-embedding the parasitic elements in the small-signal equivalent circuit. An excellent agreement between the measured and simulated S-parameters from 100 MHz to 40 GHz is achieved, which validates the feasibility of our method for extracting the bias-dependent parasitic resistances.
Crystal phase control in self-catalyzed InSb nanowires using basic growth parameter V/III ratio
(2019-09-15)
Anandan, Deepak
;
Nagarajan, Venkatesan
;
Kakkerla, Ramesh Kumar
;
Yu, Hung Wei
;
Ko, Hua Lun
In this work, the influence of V/III ratio on self-catalyzed InSb nanowire (NW) crystal structure is investigated using metal organic chemical vapor deposition. The effective balance of V/III ratio determines the change of InSb NW crystal structure from zincblende to wurtzite. Particularly, as group-V molar flow varies from 6.4 x 10(-5) to 8.0 x 10(-5) mol/min, wurtzite segment length of InSb NW increases from 16 +/- 9 nm to 89 +/- 9 nm, whereas zincblende crystal phase is observed for other molar flows. We interpret the observed phase transition to a lower surface energy of In-Sb alloy droplet than pure In-droplet, which makes triple phase line nucleation energetically favorable. This study gives insight on single growth parameter (V/III ratio) change to the InSb NW crystal control, such a technique is essential to selectively tune the crystal phase of single NW for various applications.
Growth of foreign-catalyst-free vertical InAs/InSb heterostructure nanowires on Si (111) substrate by MOCVD
(2019-01-15)
Anandan, Deepak
;
Kakkerla, Ramesh Kumar
;
Yu, Hung Wei
;
Ko, Hua Lun
;
Nagarajan, Venkatesan
In this study, growth of Au-free InAs/InSb vertical heterostructure (HS) nanowires (NWs) on highly lattice mismatched Si (1 1 1) substrate by metal organic chemical vapor deposition (MOCVD) is demonstrated. Careful selections of InSb growth parameters lead to In-rich growth regime such that direct impingement of growth precursors on top of grown InAs NW (self-assembled) stems result in axial InSb HSs nucleation on InAs stems. The observed indium (In) droplet on InSb HS NW tip shows that InSb HS growth followed a self-catalyzed growth mechanism. InSb HS axial growth rate and morphology are controlled by growth temperature and growth time. A small change in the growth parameters significantly affects In particle accumulation, particle size and its chemical composition, and thus affects the InSb nucleation on the stem. Especially, it is found that (i) growth time of less 10 min yields vertical InSb HS NW on the top of the InAs stem, (ii) as the growth time increases above 10 min, the growth turned to be InSb wrapped InAs/InSb core-shell HS due to coaxial lateral growth. High resolution transmission electron microscopy (HRTEM) study reveals that all the InSb HSs exhibit pure zinc-blende (ZB) crystal structure. The results presented here provide significant guidelines for external catalyst-free InAs/InSb HS NW growth using MOCVD on silicon (Si) substrate for various optoelectronics and electronics applications.
Low-Frequency Noise Characterization of AlGaN & x002F;GaN HEMTs and MIS-HEMTs Under UV Illumination
(2020-01-01)
Nagarajan, Venkatesan
;
Chen, Kun-Ming
;
Lin, Hsin-Yi
;
Hu, Hsin-Hui
;
Huang, Guo-Wei
The low-frequency noise characteristics of AlGaN & x002F;GaN HEMTs and MIS-HEMTs are investigated in the dark condition and under UV illumination. The test devices with a 3-& x03BC;m-thick GaN buffer and a 25-nm-thick Al_0.22Ga_0.78N barrier layer were fabricated on the silicon wafer. For MIS-HEMTs, a 25-nm-thick SiN layer was deposited as a gate dielectric. The measured low-frequency noises show a 1 & x002F;f spectrum and can be described by the carrier number fluctuation model. Different noise responses to the UV light between HEMTs and MIS-HEMTs were observed. By comparing the noise data in dark and under UV illumination, the noise sources under the gate and in the ungated gate-drain access region have been identified. From these results, we can find a design guideline to improve the noise and reliability of GaN-based devices for optoelectronic applications.
Optimization of InAs/GaSb core-shell nanowire structure for improved TFET performance
(2019-10-01)
Singh, Sankalp Kumar
;
Kakkerla, Ramesh Kumar
;
Joseph, H. Bijo
;
Gupta, Ankur
;
Anandan, Deepak
The performance of InAs/GaSb core-shell nanowire TFET is systematically investigated for the effects of intrinsic device parameters such as channel doping, shell thickness, spacer length and source offset. Device ON-current (I-ON) was chosen as the key figure of merit. It is found that I-ON improves due to improved electrostatic control achieved by the TFET with optimum shell diameter. The maximum I-ON obtained for a shell thickness of 2 nm was 33.65 mu A/mu m and a Subthreshold Swing (SS) of 12.9 mV/decade with an I-ON/I-OFF ratio of 1.49 x 10(8) for our device. Device I-ON can be further improved by adding an optimum spacer at the source-channel junction. It was also found that device ON-current is almost constant and does not get much affected by having a larger shell offset.
Study of Charge Trapping Effects on AlGaN/GaN HEMTs Under UV Illumination With Pulsed I-V Measurement
(2020-06-01)
Nagarajan, Venkatesan
;
Chen, Kun-Ming
;
Chen, Bo-Yuan
;
Huang, Guo-Wei
;
Chuang, Chia-Wei
The charge trapping effects on AlGaN/GaN HEMTs under UV illumination are investigated using the pulsed current-voltage (I-V) measurement method. The test samples are unpassivated Schottky-gate HEMTs and metal-insulator-semiconductor HEMTs (MIS-HEMTs) with SiN gate dielectric. For HEMTs, the dominant charge trapping sources are the surface trap states, whereas, for MIS-HEMTs, they are trap states in the SiN gate dielectric and GaN buffer. When these devices are shined with the UV light, the drain current increases apparently in both samples owing to the generated photocurrent. By combining the UV illumination and pulsed I-V measurement, we find out the UV light has less effect on the surface charge trapping in the unpassivated HEMTs. Moreover, in MIS-HEMTs, we observe the charge trapping in the SiN gate dielectric becomes more serious under UV illumination, whereas the charge trapping in the GaN buffer is suppressed significantly. These findings are important for designing a GaN-based HEMT for photonic applications. In addition, the different responses of the surface-, buffer-, and gate-dielectric-related charge trapping to the UV light suggest that it would be easier to distinguish the trap types by introducing the UV illumination during the pulse measurement.
Study of E-Mode AlGaN/GaN MIS-HEMT with La-silicate Gate Insulator for Power Applications
(2020-02-01)
Huang, Kuan Ning
;
Lin, Yueh-Chin
;
Lin, Jia-Ching
;
Hsu, Chia Chieh
;
Lee, Jin Hwa
An enhancement-mode (E-mode) AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT) with La2O3/SiO2 gate insulator is investigated for high power application. The La2O3/SiO2 composite oxide formed amorphous La-silicate after post deposition annealing. Good oxide film quality and excellent La-silicate/AlGaN interface properties were achieved as evidenced by the capacitance-voltage (C-V) curves and hysteresis effect of the La-silicate on AlGaN/GaN metal-oxide-semiconductor capacitors. As a result, the E-mode AlGaN/GaN MIS-HEMT with La-silicate gate insulator shows good threshold voltage (V-th) stability and demonstrated only slightly increase in the dynamic on-resistance (R-on) after high drain bias stress test. The device also exhibits high current density of 752 mA/mm, high maximum transconductance of 210 mS/mm, low subthreshold swing of 104 mV/decade, and I-ON/I-OFF = 10(7) when tested at V-DS = 10 V. Furthermore, low on-resistance of 7.6 omega mm, high breakdown voltage of 670 V, and excellent delay time of 4.2 ps were achieved, demonstrating the La-silicate MIS-HEMTs have the potential to be used for power electronic applications.