InGaN thin films grown by RF sputtering for HIT solar cells
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InGaN thin films grown by RF sputtering for HIT solar cells
Pratheesh Jakkala and Martin E Kordesch Department of Physics & Astronomy , Ohio University, Athens, OH, 45701, USA
ABSTRACT The wide range of optical band gaps of InGaN thin films led to considerable research in increasing the efficiency of solar cells. In this study, we present electrical, optical and structural properties of InGaN thin films grown by in situ rf sputtering method. Several samples of InGaN were deposited on aluminosilicate glass and silicon(111) substrates at different temperatures and varying N2 flow ratio. Growth temperatures are 35 oC, 150 oC, 200 oC. Aluminum metal contacts are deposited using DC sputtering method. Resistivity, mobility, conductivity values and their changes with respect to temperature are recorded using hall-effect measurement system. Band gap values and their changes with respect to N2 flow ratio in ( Ar+N2) mixture were calculated using UV spectrophotometer and tauc plots. Atomic composition was calculated using Energy-dispersive X-ray spectroscopy (EDX) analysis. Amorphous/crystalline nature of the samples are verified using XRD analysis. INTRODUCTION Indium gallium nitride ( InGaN), a group III-V compound semiconductor material has received a great deal of attention in the recent years. The direct band gap of InxGa(1-x)N can be varied from 0.7eV(x=1) to 3.4eV (x=0) depending on the Indium/Gallium ratio[1]. Materials with this wide range of band gap, if used properly, can absorb the entire visible solar spectrum from near infrared to deep ultraviolet and every color in between. Large difference in inter atomic spacing between InN and GaN, difference in enthalpy formations and high vapor pressure of InN compared to that of GaN are some of the problems that affect the quality of InGaN films[2]. However, these problems can be minimized by changing the parameters of growth conditions such as growth temperature, gas flow ratio, growth rate and growth pressure. Growth conditions can significantly affect the optical, electrical and structural properties of InGaN films[2]. A slight change in the growth parameters can affect the quality and properties of InGaN thin films in a large way. So it is important to understand the growth kinetics which eventually may develop the fabrication techniques for higher quality InGaN thin films. This work concentrates on growing InGaN thin films using rf magnetron sputtering method by changing the growth conditions such as growth temperature and nitrogen flow ratio to understand the change in optical (band gap), electrical and structural properties of these thin films. EXPERIMENT InGaN thin films were grown on high temperature aluminoslilicate glass and silicon(111) substrates by Rf magnetron sputtering method. Argon(Ar) and Nitrogen(N2) are used as Inert and reactive gases respectively in the sputtering process. A constant RF plasma power of 100W and a total pressure of 12 mTorr or 1.599 Pa is maintained for all samples grown irrespective of growth temperature. Parameters we changed for
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