Search query: AlN/GaN ohmic contacts

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abstract: We review the performance and discuss the potential of GaNbased field effect transistors for high power, high temperature operation. Recent Monte Carlo simulations predict that GaNbased transistors operating at high voltages may outperform GaAs based transistors even at room temperature. Our GaN/AlGaN doped channel HFETs (DC HFETs) demonstrated highest kequency operation among all wide band gap semiconductor'" devices because of excellent transport properties of two dimensional electron gas at the AlGaNIGaN heterointerface and a large sheet carrier concentration in the The I V and C V measurements and the theory of GaN AlNGaN SIS structures demonstrated a small leakage current across the AlN/GaN interface and a large conduction band discontinuity. Recently, Fan et al. lo demonstrated very low resistance ohmic contacts to n GaN (specific resistivity of 8.9x10 ohm cm2 for 1017 ~m material. Our studies demonstrated that the contact resistance rapidly decreases with an increase of the sheet electron concentration in these heterostructures. " The transient Monte Carlo simulations showed that, in spite of a higher effective mass in GaN compared to GaAs (0.22 m, compared to 0.067 m, electrons in GaN based FETs are expected to exhibit strong overshoot effects but at much higher fields than in GaAs. These calculations predict that, at high enough voltages, GaN based FETs may actually outperform GaAs based devices even at room temperature. Hence, all building blocks exist for realizing superior GaNbased field effect transistors for high frequency, high power operation.
author_names: M A Khan

Q Chen

Jialing Yang

M Zubair Anwar

M P Blasingame

Michael S Shur

Jinwook Burm

Lester F Eastman
title: RECENT ADVANCES IN 111 V NITRIDE ELECTRON DEVICES
year: 1996

abstract: Schottky and Ohmic contacts based electronics play an important role in highly sensitive detection of biomolecules and neural electric impulses, respectively. The reversible conversion between these two contacts appears especially important for multifunctional sensing by just one biosensor. Here, Schottky barrier height (SBH) is successfully tuned by triboelectric nanogenerator (TENG) and the same device is made to achieve reversible conversion between Schottky contact and Ohmic contact. In the same Schottky to Ohmic reversible (SOR) biosensor, highly sensitive detections of biomolecule (i.e. neurotransmitter) and neural electric signal are achieved at different contact states. The SOR biosensor reveals the feasibility of using one device to realize multifunctional detection. This work proposes a simple and significant method to achieve reversible tuning between the Schottky contact and Ohmic contact on one device by TENG, which exhibits great potential in developing multifunctional and high sensitivity biosensors, rectifiers, and other functional electronic devices.
author_names: Hu Li

Yaming Zhang
title: Reversible Conversion between Schottky and Ohmic Contacts for Highly Sensitive, Multifunctional Biosensors
year: 2019

abstract: Incorporation of two dimensional (2D) materials in electronic devices inevitably involves contact with metals, and the nature of this contact (Ohmic and/or Schottky) can dramatically affect the electronic properties of the assembly. Controlling these properties to reliably form low resistance Ohmic contact remains a great challenge due to the strong Fermi level pinning (FLP) effect at the interface. Herein, we employ density functional theory calculations to show that van der Waals stacking can significantly modulate Schottky barrier heights in the contact formed between multilayer InSe and 2D metals by suppressing the FLP effect. Importantly, the increase of InSe layer number induces a transition from Schottky to Ohmic contact, which is attributed to the decrease of the conduction band minimum and rise of the valence band maximum of InSe. Based on the computed tunneling and Schottky barriers, Cd3C2 is the most compatible electrode for 2D InSe among the materials studied. This work illustrates a straightforward method for developing more effective InSe based 2D electronic nanodevices.
author_names: Tao Shen

Jichang Ren

Xinyi Liu

Shuang Li

Wei Liu
title: van der Waals Stacking Induced Transition from Schottky to Ohmic Contacts: 2D Metals on Multilayer InSe.
venue: Journal of the American Chemical Society
year: 2019

abstract: Here we investigated interfacial reactions and interdiffusion of titanium/gold ohmic contacts with a tin doped single crystal b Ga2O3 (010) substrate. After annealing at 470 degC for 1 min in N2 to form an ohmic contact, we studied the interface via scanning transmission electron microscopy and transmission electron microscopy with energy dispersive X ray spectroscopy as well as electron energy loss spectroscopy. At the interface, annealing causes Ti to diffuse and oxidize, reducing Ga2O3 at the interface. This forms a defective b Ga2O3 layer of 3 5 nm that has a relatively high Ti concentration. Above this is a 3 5 nm layer of Ti TiOx that is partially lattice matched to the b Ga2O3 substrate. The thermodynamic favorability of these redox reactions was explained by calculating Gibbs free energies of the reactions. In addition, the anneal causes interdiffusion of Ti and Au, until Au is in contact with the thin Ti TiOx layer. A layer of Ti rich nanocrystals, around 5 nm in diameter, is formed within the Au Ti intermixed matrix, about 3 nm above the Ti TiOx layer. Based on these observations, the ohmic properties are tentatively attributed to the interdiffusion of Ti and Au and the resulting thin Ti TiOx layer, which helps band alignment. In addition, lattice matching of the defective Ga2O3 and Ti TiOx layers to b Ga2O3 facilitates the transport of carriers. A physical understanding of Ti/Au metallization can provide insights into future materials selection for thermally stable contacts in b Ga2O3 power devices.
author_names: Ming-Hsun Lee

Rebecca L Peterson
title: Interfacial reactions of titanium/gold ohmic contacts with Sn doped b Ga2O3
venue: APL Materials
year: 2019

abstract: We report silicon delta doped <inline formula> <tex math notation="LaTeX"\beta /tex math>/inline formula> Ga<sub>2</sub>O<sub>3</sub> metal semiconductor field effect transistors (MESFETs) with source drain ohmic contacts formed by patterned regrowth of n type Ga<sub>2</sub>O<sub>3</sub> We show that regrown n type contacts can enable a lateral low resistance contact to the two dimensional electron gas channel, with contact resistance lower than <inline formula> <tex math notation="LaTeX"$1.5~\Omega /tex math>/inline formula> mm. The fabricated MESFET has a peak drain current <inline formula> <tex math notation="LaTeX"{I} _{D,\text{MAX} /tex math>/inline formula> of 140 mA/mm, transconductance <inline formula> <tex math notation="LaTeX"{g} _{m} /tex math>/inline formula> of 34 mS/mm, and 3 terminal off state breakdown voltage of 170 V. The proposed device structure could provide a promising path towards vertically scaled <inline formula> <tex math notation="LaTeX"\beta /tex math>/inline formula> Ga<sub>2</sub>O<sub>3</sub> field effect transistors.
author_names: Zhanbo Xia

Chandan Joishi

Sriram Krishnamoorthy

Sanyam Bajaj

Yuewei Zhang

Mark R Brenner

Saurabh Lodha

Siddharth Rajan
title: Delta Doped \beta$ Ga2O3 Field Effect Transistors With Regrown Ohmic Contacts
venue: IEEE Electron Device Letters
year: 2018

abstract: We report high performance WSe2 phototransistors with two dimensional (2D) contacts formed between degenerately p doped WSe2 and undoped WSe2 channel. A photoresponsivity of ~600 mA/W with a high external quantum efficiency up to 100% and a fast response time (both rise and decay times) shorter than 8 ms have been achieved concurrently. More importantly, our WSe2 phototransistor exhibits a high specific detectivity ~1013 Jones) in vacuum, comparable or higher than commercial Si and InGaAs based photodetectors. Further studies have shown that the high photoresponsivity and short response time of our WSe2 phototransistor are mainly attributed to the lack of Schottky barriers between degenerately p doped WSe2 source/drain contacts and undoped WSe2 channel, which can reduce the RC time constant and carrier transit time of a photodetector. Our experimental results provide an accessible strategy to achieve high performance WSe2 phototransistor architectures by improving their electrical transport and photocurrent generation simultaneously, opening up new avenues for engineering future 2D optoelectronic devices.
author_names: Tianjiao Wang

Kraig Andrews

Arthur Bowman

Tu Hong

Michael R Koehler

Jiaqiang Yan

David G Mandrus

Zhixian Zhou

Yaqiong Xu
title: High Performance WSe2 Phototransistors with 2D/2D Ohmic Contacts.
venue: Nano letters
year: 2018

abstract: AlGaN/GaN high electron mobility transistors on semi insulating bulk ammonothermal GaN have been investigated. By application of regrown ohmic contacts, the problem with obtaining low resistance ohmic contacts to low dislocation high electron mobility transistor (HEMT) structures was solved. The maximum output current was about 1 A/mm and contact resistances was in the range of 0.3 0.6 O*mm. Good microwave performance was obtained due to the absence of parasitic elements such as high access resistance.
author_names: Wojciech Wojtasiak

Marcin Goralczyk

Daniel Gryglewski

Marcin Zajac

Robert Kucharski

Pawel Prystawko

Anna Piotrowska

Marek Ekielski

Eliana Kaminska

Andrzej Taube

Marek Wzorek
title: AlGaN/GaN High Electron Mobility Transistors on Semi Insulating Ammono GaN Substrates with Regrown Ohmic Contacts
venue: Micromachines
year: 2018

abstract: While thermodynamic detailed balance limits the maximum power conversion efficiency of a solar cell, the quality of its contacts can further limit the actual efficiency. The criteria for good contacts to organic semiconductors, however, are not well understood. Here, by tuning the work function of poly(3,4 ethylenedioxythiophene) hole collection layers in fine steps across the Fermi level pinning threshold of the model photoactive layer, poly(3 hexylthiophene):phenyl C61 butyrate methyl ester, in organic solar cells, we obtain direct evidence for a non ohmic to ohmic transition at the hole contact that lies 0.3 eV beyond its Fermi level pinning transition. This second transition corresponds to reduction of the photocurrent extraction resistance below the bulk resistance of the cell. Current detailed balance analysis reveals that this extraction resistance is the counterpart of injection resistance, and the measured characteristics are manifestations of charge carrier hopping across the interface. Achieving ohmic transition at both contacts is key to maximizing fill factor without compromising open circuit voltage nor short circuit current of the solar cell.The importance of ohmic contacts for organic solar cells has been recognized, but how the transition to ohmic behavior occurs is unknown. Tan et al. show that this transition happens separately beyond Fermi level pinning, when the interfacial contact resistivity becomes sufficiently low.
author_names: Jun-Kai Tan

Rui-Qi Png

Chao Zhao

Peter K H Ho
title: Ohmic transition at contacts key to maximizing fill factor and performance of organic solar cells
venue: Nature Communications
year: 2018

abstract: We report on the electrical and microstructural characterization of Au free Ti/Al/Ti/TiN contacts for AlGaN/GaN heterostructures. Ultra low Au free ohmic contact has been obtained with contact resistance and specific contact resistivity as low as <inline formula> <tex math notation="LaTeX"$0.21~\Omega \cdot \text{mm} /tex math>/inline formula> and <inline formula> <tex math notation="LaTeX"{1.16}\times {10} 6} \Omega \cdot \text{cm}{2} /tex math>/inline formula> respectively. The ohmic alloy temperature is reduced as low as 550 degC by pre ohmic recess of the AlGaN barrier and optimization of the thickness of bottom Ti layer. We found that interfacial layer formation of AlN between the ohmic metal and AlGaN surface is crucial to realize a low contact resistance with reduced low annealing temperature by a combination of electrical <inline formula> <tex math notation="LaTeX"{I} /tex math>/inline formula> <inline formula> <tex math notation="LaTeX"{V} /tex math>/inline formula> characterization and high resolution transmission electron microscopy analysis. Furthermore, we suggest a hypothesis that the bottom Ti layer plays a catalytic role for the Al N reaction with optimized thickness.
author_names: Jinhan Zhang

Xuanwu Kang

Xinhua Wang

Sen Huang

C Chen

Ke Wei

Yingkui Zheng

Qi Zhou

Wanjun Chen

Bo Zhang

Xinyu Liu
title: Ultralow Contact Resistance Au Free Ohmic Contacts With Low Annealing Temperature on AlGaN/GaN Heterostructures
venue: IEEE Electron Device Letters
year: 2018

abstract: Most semiconductor devices require low resistance ohmic contact to p type doped regions. In this work, we present a semi salicide process that forms low resistance contacts ~10 4 O cm2) to epitaxially grown p type >5x1018 cm 3) 4H SiC at temperatures as low as 600 degC using rapid thermal processing (RTP) The first step is to self align the nickel silicide (Ni2Si) at 600 degC. The second step is to deposit aluminium on top of the silicide, pattern it and then perform a second annealing step in the range 500 degC to 700 degC.
author_names: Mattias Ekstrom

Shuoben Hou

Hossein Elahipanah

Arash Salemi

Mikael Ostling

Carl-Mikael Zetterling
title: Low Temperature Ni Al Ohmic Contacts to p Type 4H SiC Using Semi Salicide Processing
year: 2018