成果報告書詳細
管理番号20160000000300
タイトル*平成27年度中間年報 「高性能・高信頼性太陽光発電の発電コスト低減技術開発/革新的新構造太陽電池の研究開発/超高効率・低コストIIIーV化合物太陽電池モジュールの研究開発(窒化物ハイブリッド結晶成長)」
公開日2017/4/1
報告書年度2015 - 2015
委託先名国立大学法人名古屋大学
プロジェクト番号P15003
部署名新エネルギー部
和文要約
英文要約Title:Development of high performance and reliable PV modules to reduce levelized cost of energy/ Research and Development of innovative new structure solar cells/ Research and Development of ultra-high efficiency and low-cost III-V compound semiconductor solar cell modules(Growth technology for nitride top cell) (FY2015-FY2017)FY2015 Annual Report

Abstract
III-nitrides show direct bandgap from 0.6 to 6eV, therefore we have used it as optical devices. We will achieve the top cell of the tandem type solar cell by using high In content InGaN crystal. But the crystal quality of InGaN with high In content is not so good because the lattice mismatch of GaN and InGaN is quite large. It causes high compressive strain in the InGaN layer, as a results, the large piezoelectric field in the InGaN film was occurred. Low growth temperature of InGaN also degrades the crystal quality. In this study, we try to get InGaN on -c-face GaN or (1-101)GaN on which we could reduce the piezo-electric field or get high In content InGaN at high temperature.
Experimental procedure and results
I. The crystal growth of InGaN layer on (1-101)GaN/Si substrate
We made the SiO2 stripe pattern on 7degree off (001)Si substrate. Then (111)Si facet was obtained in the KOH solution. The selective MOVPE growth was followed then we got the (1-101)GaN. An InGaN layer was grown on that template. We found that the high temperature growth is necessary to realize high quality InGaN. Then thick InGaN growth was performed under the growth rate of 10nm/min for 1.25-4min. The PL peak wavelength is around 540, 550, 600nm for 1.25, 2.5 and 4min sample, respectively. For the 4min sample, In composition is reach to over 35%, and keep the high luminous intensity. The misfit dislocation between interface of GaN and InGaN was inherited from GaN layer and it caused the decline of the (1-101) InGaN plane. By this process, InGaN strain was relaxed but dislocation density did not increase. Therefore the luminous intensity was kept for even if the InGaN layer is as thick as 40nm.
II. Solar cell simulation of polar or non-polar GaN
A simulation was performed in order to obtain solar cell characteristics in the polar face. We used the In composition varies from 10 to 30%. For 10%, a sharp drop of current at 1.5V is observed. A piezoelectric field gave the reverse bias to inside electric field, as a result, it was canceled over 1.5V and formed flat band. Its trend is seen remarkably at high In composition region and current was gradually decreased. This is because a very large piezoelectric field prevented current to escape. Next, we investigated the comparison of the solar cell characteristics of the c-plane and the non-polar plane (m plane or a plane). It was found that solar cell which was grown on the non-polar GaN showed normal characteristics. Since the piezoelectric field can be reduced to below about 1/3 for (1-101) plane, it is considered an effective growth surface.
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