Browsing by Author "Kakkerla, Ramesh Kumar"

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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.
Crystal structure control of Au-free InAs and InAs/GaSb heterostucture nanowires grown on Si (111) by metal-organic chemical vapor deposition
(2019-01-01)
Kakkerla, Ramesh Kumar
;
Anandan, Deepak
;
Singh, Sankalp Kumar
;
Yu, Hung Wei
;
Lee, Ching-Ting
In this letter, the growth of gold-free GaSb on various InAs nanowire (NW) crystal structures using metal-organic chemical vapor deposition is demonstrated. The GaSb was grown radially and axially on wurtzite (WZ), zinc-blend (ZB) and polytype (mixture of WZ and ZB) InAs NWs. The effect of the various InAs crystal structures on GaSb was studied. This study demonstrates the control of the crystal growth of InAs and InAs/GaSb heterostructure NWs through the optimization of growth parameters and crystal transfer from core to shell, such techniques are necessary for the growth of NWs for future nanoelectronic device applications, such as TFET. (C) 2018 The Japan Society of Applied Physics
Effect of Two-Step Metal Organic Chemical Vapor Deposition Growth on Quality, Diameter and Density of InAs Nanowires on Si (111) Substrate
(2018-02-01)
Yu, Hung Wei
;
Anandan, Deepak
;
Hsu, Ching Yi
;
Hung, Yu Chih
;
Su, Chun Jung
High-density (similar to 80/um(2)) vertical InAs nanowires (NWs) with small diameters (similar to 28 nm) were grown on bare Si (111) substrates by means of two-step metal organic chemical vapor deposition. There are two critical factors in the growth process: (1) a critical nucleation temperature for a specific In molar fraction (approximately 1.69 x 10(-5) atm) is the key factor to reduce the size of the nuclei and hence the diameter of the InAs NWs, and (2) a critical V/III ratio during the 2nd step growth will greatly increase the density of the InAs NWs (from 45 mu m(-2) to 80 mu m(-2)) and at the same time keep the diameter small. The high-resolution transmission electron microscopy and selected area diffraction patterns of InAs NWs grown on Si exhibit a Wurtzite structure and no stacking faults. The observed longitudinal optic peaks in the Raman spectra were explained in terms of the small surface charge region width due to the small NW diameter and the increase of the free electron concentration, which was consistent with the TCAD program simulation of small diameter (< 40 nm) InAs NWs.
Growth and characterization of high quality N-type GaSb/GaAs heterostructure by IMF growth mode using MOCVD for low power application
(2017-10-16)
Hsiao, Chih Jen
;
Kakkerla, Ramesh Kumar
;
Chang, Po Chun
;
Lumbantoruan, Franky Juanda
;
Lee, Tsu Ting
In this study, we demonstrate the growth of a 150-nm-thick GaSb layer on a GaAs substrate with excellent film quality using the interfacial misfit dislocation growth mode by the Metal-Organic Chemical Vapor Deposition technique. The n-type GaSb epilayer grown on the GaAs substrate has a low threading dislocation density of 3.2 x 10(6) cm(-2) and a surface roughness of approximately 0.8 nm. A high carrier mobility up to 4600 cm(2) V-1 s(-1) with a carrier concentration of 1.2 x 10(17) cm(-3) is achieved in this study. The fabricated Al2O3/GaSb/GaAs MOSCAP demonstrated excellent capacitance-voltage (C-V) characteristics with a small frequency dispersion of approximately 2.8%/decade. The results demonstrate the potential of high-mobility Sb-based materials on GaAs for p-type channel CMOS applications in the future. Published by AIP Publishing.
Growth and Crystal Structure Investigation of InAs/GaSb Heterostructure Nanowires on Si Substrate
(2018-11-01)
Kakkerla, Ramesh Kumar
;
Hsiao, Chih-Jen
;
Anandan, Deepak
;
Singh, Sankalp Kumar
;
Chang, Sheng-Po
We report gold-free growth of vertically aligned InAs/GaSb heterostructure nanowires (NWs) on Si(111) substrate by metal organic chemical vapor deposition technique. The effect of growth temperature on morphology and growth rate for InAs and InAs/GaSb heterostructure NWs were investigated. A combination of high material flow rates and optimum temperature (600 degrees C) has given better crystal quality of InAs nanowires. The morphology and shell thickness of NWs as observed by scanning electron microscope and transmission electron microscope (TEM) measurements can be tuned by the growth temperature. Electron microscopy also shows the formation of GaSb both in radial and axial directions outside the InAs NW core at certain growth temperatures. Crystal structure of InAs and InAs/GaSb heterostructure NWs was analyzed by high-resolution TEM and fast Fourier transform analysis. Using good crystalline InAs core grown at optimized growth temperature (600 degrees C), GaSb shell has been grown without any misfit dislocations at the core-shell interface. Basic electrical properties have been measured by forming ohmic contacts. I-V characteristics exhibit linear response indicating good ohmic behavior. These results show good control over InAs NWs growth, the GaSb shell thickness, and its crystal quality, which are essential for future nanoelectronic devices such as tunneling FET.
Growth and Crystal Structure Investigation of Self-catalyst InAs/GaSb Heterostructure Nanowires on Si substrate
(2017-01-01)
Kakkerla, Ramesh Kumar
;
Hsiao, Chih-Jen
;
Anandan, Deepak
;
Singh, Sankalp Kumar
;
Chang, Edward Yi
We demonstrate the self-catalyst (SC) growth of vertically aligned InAs and InAs/GaSb heterostructure nanowires on Si(111) substrate by Metal Organic Chemical Vapor Deposition (MOCVD). The effect of growth temperature on morphology and growth rate for SC InAs and InAs/GaSb heterostructure nanowires (NWs) were investigated. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) measurements revealed the morphology and shell thickness can be tuned by the growth temperature. Electron microscopy also shows the formation of GaSb both in radial and axial directions outside the SC InAs NW core at certain growth temperatures. Crystal structure of InAs/GaSb heterostructure nanowires was also discussed. These results show that the control over SC InAs NWs growth, the GaSb shell thickness and it's crystal quality was achieved which is essential for future nano electronic devices such as TFET.
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.
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.
Temperature effect on the growth of Au-free InAs and InAs/GaSb heterostructure nanowires on Si substrate by MOCVD
(2018-05-15)
Kakkerla, Ramesh Kumar
;
Anandan, Deepak
;
Hsiao, Chih-Jen
;
Yu, Hung Wei
;
Singh, Sankalp Kumar
We demonstrate the growth of vertically aligned Au-free InAs and InAs/GaSb heterostructure nanowires on Si (1 1 1) substrate by Metal Organic Chemical Vapor Deposition (MOCVD). The effect of growth temperature on the morphology and growth rate of the InAs and InAs/GaSb heterostructure nanowires (NWs) is investigated. Control over diameter and length of the InAs NWs and the GaSb shell thickness was achieved by using growth temperature. As the GaSb growth temperature increase, GaSb radial growth rate increases due to the increase in alkyl decomposition at the substrate surface. Diffusivity of the adatoms increases as the GaSb growth temperature increase which results in tapered GaSb shell growth. Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) measurements revealed that the morphology and shell thickness can be tuned by the growth temperature. Electron microscopy also shows the formation of GaSb both in radial and axial directions outside the InAs NW core can be controlled by the growth temperature. This study demonstrates the control over InAs NWs growth and the GaSb shell thickness can be achieved through proper growth temperature control, such technique is essential for the growth of nanowire for future nano electronic devices, such as Tunnel FET. (C) 2018 Elsevier B.V. All rights reserved.