Effect of oxygen plasma treatment on the electrical characteristics of Pt/n-type Si Schottky diodes

Janardhanam, V.,Jyothi, I.,Yuk, S. H.,Choi, C. J.,Lee, S. N.,Reddy, V. R. 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.

<P>The electrical properties of Pt/n-type Si Schottky diodes fabricated from n-type Si wafers subjected to an oxygen (O-2) plasma treatment were investigated as a function of the power of the O-2 plasma. The Pt/n-type Si Schottky diode with an O-2 plasma treatment at a power of 100 W showed better rectifying characteristics with increasing barrier height and decreasing ideality factor compared to the conventional Pt/n-type Si Schottky diodes. This could be attributed to an improvement in the interface homogeneity associated with damage-free surface smoothing driven by the O-2 plasma treatment at a power of 100 W. On the other hand, with increasing power of the O-2 plasma for powers above 150 W, the barrier height decreased and the leakage current increased, indicating degradation of the device performance. The degradation in the rectifying properties after the O-2 plasma treatment at a higher plasma power in excess of 150 W could be associated with increases in the series resistance and the interface state density caused by plasma-induced damage to the Si surface.</P>

Fermi-level depinning in metal/Ge interface using oxygen plasma treatment

Janardhanam, Vallivedu,Yun, Hyung-Joong,Jyothi, Inapagundla,Yuk, Shim-Hoon,Lee, Sung-Nam,Won, Jonghan,Choi, Chel-Jong Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.463 No.-

<P><B>Abstract</B></P> <P>Oxygen (O<SUB>2</SUB>) plasma treatment on germanium (Ge) surface was employed to depin Fermi-level in Al/n-type Ge interface. The Al contact to n-type Ge without and with O<SUB>2</SUB> plasma treatments for 1 and 2 min showed rectifying characteristics despite the low work function of Al, which could be associated with the Fermi-level pinning. An increase in O<SUB>2</SUB> plasma treatment time resulted in a decrease in Schottky barrier height along with the improvement of the homogeneity of Schottky interface. On the other hand, Al contact to O<SUB>2</SUB> plasma-treated n-type Ge for 3 min exhibited Ohmic behavior, implying the depinning of Fermi-level in Al/n-type Ge interface. A transition from rectifying to Ohmic behavior observed in Al/n-type Ge contact with O<SUB>2</SUB> plasma treatment for 3 min could be attributed to the more homogenous and stoichiometric formation of Ge-oxide layer. Such a high quality Ge-oxide layer effectively passivated unsatisfied surface states in Ge, which could be responsible for Fermi-level depinning of Ge.</P> <P><B>Highlights</B></P> <P> <UL> <LI> O<SUB>2</SUB> plasma treatment on Ge surface was employed to depin Fermi-level of Ge interface. </LI> <LI> Transition from Schottky to Ohmic behavior was observed in Al/n-type Ge with O<SUB>2</SUB> plasma treatment for 3 min. </LI> <LI> An increase in O<SUB>2</SUB> plasma treatment time led to the improved homogeneity of Schottky interface. </LI> <LI> More homogenous and stoichiometric Ge-oxide layer was formed after O<SUB>2</SUB> plasma treatment for 3 min. </LI> <LI> Ge surface passivation through Ge-oxide layer could be a main cause of depinning the Fermi-level of Ge. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Rectifying and breakdown voltage enhancement of Au/n-GaN Schottky diode with Al-doped ZnO films and its structural characterization

Janardhanam, V.,Jyothi, I.,Lee, Sung-Nam,Reddy, V. Rajagopal,Choi, Chel-Jong Elsevier S.A. 2019 Thin Solid Films Vol.676 No.-

<P><B>Abstract</B></P> <P>Radio frequency magnetron sputtered Al-doped zinc oxide (AZO) thin films were formed on n-type gallium nitride (GaN). X-ray diffraction reflections and Raman modes confirmed the formation of the AZO films. The optical band gap of the deposited AZO film was found to be 3.31 eV and exhibited a fairly smooth surface and continuous growth across the surface with a grainy structure. The Au/AZO/n-GaN heterojunction Schottky diode was fabricated and investigated the influence of the presence of AZO layer in Au/n-GaN Schottky diode, characterizing its electrical and breakdown voltage properties. The AZO layer led to an excellent improvement in the rectifying behavior with an increase in barrier height of the Au/n-GaN Schottky diode from 0.69 to 0.90 eV. Reverse breakdown voltage of the Au/n-GaN Schottky diode and Au/AZO/n-GaN heterojunction diode were obtained to be 86 and 232 V, respectively, without any edge termination methods. The AZO layer effectively reduced the interface states in the Au/n-GaN Schottky diodes. Schottky and Poole-Frenkel emission mechanisms dominated the reverse current in Au/n-GaN Schottky diode and Au/AZO/n-GaN heterojunciton diode, respectively. The results signify the importance of the metal-insulator-semiconductor structure and in particular the AZO layer in reducing the leakage current and improving the device performance. A further improvement in breakdown voltage can be achieved by employing field plate and guard-ring structures for edge termination.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabricated Au/Al-doped ZnO (AZO)/n-GaN heterojunction diode by sputtering AZO films. </LI> <LI> X-ray diffraction and Raman modes confirmed the formation of AZO films. </LI> <LI> AZO films deposited on GaN exhibited a fairly smooth surface with a grainy structure. </LI> <LI> Excellent improvement in rectification of Au/n-GaN Schottky diode by AZO insertion. </LI> <LI> Breakdown voltage of Au/n-GaN Schottky diode rises from 86 to 232 V by AZO insertion. </LI> </UL> </P>

Double Gaussian barrier distribution of permalloy (Ni_0.8Fe_0.2) Schottky contacts to n-type GaN

Janardhanam, V.,Jyothi, I.,Sekhar Reddy, P.R.,Cho, Jaehee,Cho, Jeong-Mook,Choi, Chel-Jong,Lee, Sung-Nam,Rajagopal Reddy, V. Elsevier 2018 Superlattices and microstructures Vol.120 No.-

<P><B>Abstract</B></P> <P>The temperature-dependent current-voltage (<I>I-V</I>) characteristics of permalloy (Ni<SUB>0.8</SUB>Fe<SUB>0.2</SUB>) Schottky contacts to n-type GaN have been investigated. Magnetization measurements revealed the ferromagnetic behavior of Ni<SUB>0.8</SUB>Fe<SUB>0.2</SUB> film on n-type GaN. The Schottky barrier parameters, such as the barrier height and ideality factor, determined by thermionic emission depended on the measurement temperature, suggesting the presence of lateral inhomogeneity in the Schottky barrier. The experimental data modified by the thermionic emission model along with a Gaussian distribution of the barrier heights indicated the presence of a double Gaussian barrier distribution in the Ni<SUB>0.8</SUB>Fe<SUB>0.2</SUB>/n-type GaN Schottky contact. The mean barrier heights and standard deviations for each Gaussian distribution were 0.84 & 1.32 eV and 0.10 & 0.17 eV over temperature range of 125–200 K and 225–400 K, respectively. The noise spectral density of the current fluctuations measured as a function of frequency (<I>f</I>) at room temperature followed a 1/<I>f</I> <SUP> <I>γ</I> </SUP> dependence with a <I>γ</I> value close to unity, irrespective of the applied forward bias. The 1/<I>f-</I>type noise was attributed to the barrier inhomogeneity existing at the Ni<SUB>0.8</SUB>Fe<SUB>0.2</SUB>/n-type GaN Schottky interface as revealed from the temperature-dependent <I>I</I>–<I>V</I> characteristics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The Ni<SUB>0.8</SUB>Fe<SUB>0.2</SUB>/n-type GaN structure showed ferromagnetic behavior. </LI> <LI> <I>I</I>–<I>V</I>–<I>T</I> characteristics of permalloy (Ni<SUB>0.8</SUB>Fe<SUB>0.2</SUB>)/n-GaN Schottky diodes were studied. </LI> <LI> Thermionic emission model with a Gaussian distribution of barriers indicates double barrier distribution. </LI> <LI> At 300 K, current noise spectral density against frequency (<I>f</I>) showed a 1/<I>f</I> dependence. </LI> <LI> 1/<I>f-</I>type noise was attributed to barrier inhomogeneity at the Ni<SUB>0.8</SUB>Fe<SUB>0.2</SUB>/n-type GaN Schottky interface. </LI> </UL> </P>

Fermi-level depinning in germanium Schottky junction using nitrogen plasma treatment

Janardhanam, V.,Yun, H.-J.,Jyothi, I.,Lee, H.-K.,Lee, S.-N.,Won, J.,Choi, C.-J. Institution of Electrical Engineers 2018 Electronics letters Vol.54 No.14

<P>Fermi-level depinning in germanium (Ge) through nitrogen (N-2) plasma treatment is demonstrated. The Ge surface was exposed to N-2 plasma for 1 min without heat treatment, resulting in the formation of 2.5 nm-thick GeOxNy layer with uniform surface and interface morphologies. Ohmic and Schottky behaviours were obtained for Al contacts to N-2 plasma-treated n- and p-type Ge with barrier heights of 0.09 and 0.40 eV, respectively. Fermi-level depinning could be attributed to the reduction in interface states caused by the passivation of Ge surface by highly uniform GeOxNy layer.</P>

Microstructural Evolution and Electrical Characteristics of Er-germanides Formed on Ge Substrate

Janardhanam, V.,Moon, Kyungwon,Kim, Jin-Sung,Yi, Min-Su,Ahn, Kwang-Soon,Choi, Chel-Jong The Electrochemical Society 2011 Journal of the Electrochemical Society Vol.158 No.8

Electrical Properties and Carrier Transport Mechanism of Au/n-GaN Schottky Contact Modified Using a Copper Pthalocyanine (CuPc) Interlayer

Janardhanam, V.,Jyothi, I.,Lee, J.-H.,Kim, J.-Y.,Reddy, V.R.,Choi, C.-J. JAPAN INSTITUTE OF METALS 2014 MATERIALS TRANSACTIONS Vol.55 No.5

We investigated the electrical characteristics of Au/n-GaN Schottky rectifier incorporating a copper pthalocyanine (CuPc) interlayer using current voltage (I-V), capacitance voltage (C-V) and conductance voltage (G-V) measurements. The barrier height of the Au/CuPc/n-GaN Schottky contact was higher than that of the Au/n-GaN Schottky diode, indicating that the CuPc interlayer influenced the space charge region of the n-GaN layer. The series resistance of Au/CuPc/n-GaN Schottky contact extracted from the C-V and G-V methods was dependent on the frequency. In addition, the series resistance obtained from C V and G V characteristics was comparable to that from Cheung's method at sufficiently high frequencies and in strong accumulation regions. The forward log / log V plot of Au/CuPc/n-GaN Schottky contact exhibited four distinct regions having different slopes, indicating different conduction mechanisms in each region. In particular, at higher forward bias, the trap-filled space-charge-limited current was the dominant conduction mechanism of Au/CuPc/n-GaN Schottky contact, implying that the most of traps were occupied by injected carriers at high injection level.

Conduction Mechanism of Se Schottky Contact to n-Type Ge

Janardhanam, V.,Yang-Kyu Park,Hyung-Joong Yun,Kwang-Soon Ahn,Chel-Jong Choi IEEE 2012 IEEE electron device letters Vol.33 No.7

<P>The conduction mechanism of Se/n-type-Ge Schottky diodes is investigated using temperature-dependent current-voltage (<I>I</I>- <I>V</I>) characteristics. The presence of microscopic inhomogeneity at the Se/Ge interface could be the primary cause of the differences between the barrier heights measured from the <I>I</I>-<I>V</I> and capacitance-voltage (<I>C</I>-<I>V</I> ) characteristics. The position of the quasi-Fermi level suggested the dominance of thermionic emission in the forward bias region. The electric field dependence of the reverse current revealed that Schottky emission, along with the generation mechanism, has dominance over the current conduction in the reverse bias region.</P>

Modification of Schottky barrier properties of Al/p-type Si Schottky rectifiers with graphene-oxide-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) interlayer

Janardhanam, Vallivedu,Jyothi, Inapagundla,Yuk, Shim-Hoon,Choi, Chel-Jong,Yun, Hyung-Joong,Won, Jonghan,Hong, Won-Gi,Lee, Sung-Nam,Rajagopal Reddy, Varra American Institute of Physics 2017 Journal of Vacuum Science & Technology. B Vol.35 No.2

Electrical properties of a Cu-germanide Schottky contact to n-type Ge depending on its microstructural evolution driven by rapid thermal annealing

Janardhanam, V.,Jyothi, I.,Lee, J.H.,Yun, H.J.,Won, J.,Lee, Y.B.,Lee, S.N.,Choi, C.J. Elsevier Sequoia 2017 THIN SOLID FILMS - Vol.632 No.-

The electrical properties of Cu-germanide(Cu<SUB>3</SUB>Ge)/n-type Ge Schottky contacts formed as a result of a solid state reaction between Cu and n-type Ge were investigated as a function of the rapid thermal annealing (RTA) temperature and correlated with its microstructural evolution driven by the RTA process. The variations of the barrier height of Cu<SUB>3</SUB>Ge/n-type Ge Schottky rectifiers caused by the RTA process were determined using current-voltage (I-V) and capacitance-voltage (C-V) methods. The Cu<SUB>3</SUB>Ge film formed after annealing at 400<SUP>o</SUP>C exhibited a relatively uniform surface and interface morphology. This led to the formation of a laterally homogenous Schottky barrier in the Cu<SUB>3</SUB>Ge/n-type Ge Schottky diode, resulting in an improvement of its rectifying I-V behavior. On the other hand, after annealing above 500<SUP>o</SUP>C, the Cu<SUB>3</SUB>Ge film was severely agglomerated without film continuity and eventually evolved into isolated islands at 600<SUP>o</SUP>C. Such structural degradation of Cu<SUB>3</SUB>Ge led to a rapid decrease in the barrier height and an increase in the reverse leakage current of the Cu<SUB>3</SUB>Ge/n-type Ge Schottky diode. The electric field dependence of the reverse current showed that the reverse leakage current in the Cu<SUB>3</SUB>Ge/n-type Ge Schottky diodes was dominated by a Poole-Frenkel emission mechanism, regardless of the RTA temperatures.