Behavior of deep level defects on voltage-induced stress of Cu(In,Ga)Se₂ solar cells

Lee, D.W.,Cho, S.E.,Jeong, J.H.,Cho, H.Y. Elsevier 2015 THIN SOLID FILMS - Vol.582 No.-

<P><B>Abstract</B></P> <P>The behavior of deep level defects by a voltage-induced stress for CuInGaSe<SUB>2</SUB> (CIGS) solar cells has been investigated. CIGS solar cells were used with standard structures which are Al-doped ZnO/i-ZnO/CdS/CIGSe<SUB>2</SUB>/Mo on soda lime glass, and that resulted in conversion efficiencies as high as 16%. The samples with the same structure were isothermally stressed at 100°C under the reverse voltages. The voltage-induced stressing in CIGS samples causes a decrease in the carrier density and conversion efficiency. To investigate the behavior of deep level defects in the stressed CIGS cells, photo-induced current transient spectroscopy was utilized, and normally 3 deep level defects (including 2 hole traps and 1 electron trap) were found to be located at 0.18eV and 0.29eV above the valence band maximum (and 0.36eV below the conduction band). In voltage-induced cells, especially, it was found that the decrease of the hole carrier density could be responsible for the increase of the 0.29eV defect, which is known to be observed in less efficient CIGS solar cells. And the carrier density and the defects are reversible at least to a large extent by resting at room-temperature without the bias voltage. From optical capture kinetics in photo-induced current transient spectroscopy measurement, the types of defects could be distinguished into the isolated point defect and the extended defect. In this work, it is suggested that the increase of the 0.29eV defect by voltage-induced stress could be due to electrical activation accompanied by a loss of positive ion species and the activated defect gives rise to reduction of the carrier density.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We investigated behavior of deep level defects by voltage-induced stress. </LI> <LI> Defect generation could affect the decrease of the conversion efficiency of cells. </LI> <LI> Defect generation could be electrically activated by a loss of positive ion species. </LI> <LI> Type of defects could be studied with models of point defects and extended defects. </LI> <LI> Changes of carrier density and defects are reversible at least to a large extent. </LI> </UL> </P>

"후열처리 분위기에 따른 깊은 준위결함의 변화가 Ga2O3/SiC 이종접합 다이오드에 미치는 영향 분석"

정승환,신명철,Mathieu Jarry,구상모 한국전기전자학회 2024 전기전자학회논문지 Vol.28 No.1

"본 연구에서는 다양한 가스 분위기에서 후열처리를 진행한 후 Ga2O3/SiC 이종접합 다이오드의 깊은 준위 결함 변화를 Deep Level Transient Spectroscopy(DLTS) 기법으로 분석하여 깊은 준위 결함의 변화가 Ga2O3/SiC 이종접합 소자의 전기적 특성에미치는 영향을 조사하였다. 또한, J-V 측정 및 Hall 측정을 통한 전기적 특성 분석을 실시하였고, N2 분위기에서 열처리된 소자에서3.06 × 10-2 A/cm2로 가장 높은 on-state current가 측정되었으며, carrier concentration은 3.8 × 1014 cm-3로 증가하는것이 관측되었다. 이는 후열처리 분위기에 따른 깊은 준위 결함의 변화가 전기적 특성에 영향을 미칠 수 있음을 시사한다." "In this research, we explored the influence of post-annealing atmospheres on the electrical properties of Ga2O3/SiC heterojunction diodes. We fabricated Ga2O3/SiC heterojunction diodes by RF sputtering and after the fabrication the post-annealing in various gas atmospheres was performed. We measured the changes in deep-level defects using Deep Level Transient Spectroscopy (DLTS) and we conducted an electrical characteristic of J-V measurement and Hall measurement to analyzed the effects of annealing atmosphere on Ga2O3/SiC heterojunction diode. In the N2 annealed devices, the highest on-state current was measured as 3.06 × 10-2 A/cm^2, and an increase in carrier concentration of 3.8 × 1014 cm-3 was observed. This confirms that the variations in deep level defects due to the post-annealing atmosphere can influence the electrical properties."

Ga 증기압 변화에 따른 GaN 박막의 누선전류 원인에 관한 연구

박병권,오정은,이상태,황지원,김문덕,김송강 한국물리학회 2016 새물리 Vol.66 No.11

We have investigated the origin of the leakage current in GaN films grown on AlN/Si(111) substrates by using plasma-assisted molecular beam epitaxy with various gallium fluxes. Scanning electron microscopy images revealed that the GaN film grown under a N-rich condition showed large hexagonal defects and a roughened surface. On the contrary, a flat surface with pinholes was obtained for the GaN film grown under a Ga-rich condition. Rocking-curve measurement of X-ray diffraction revealed that line-defect density decreased with increasing Ga flux. Electrical defect levels related with line (0.46 eV) and point (0.77 eV) defects were found by using deep-level transient spectroscopy. Moreover, line-defect density in the GaN film grown under a Ga-rich condition is almost constant compared to GaN films grown under N-rich or N/Ga$\sim$1 conditions. The experimental results indicated that lateral growth can be induced during the initial stage grown under a Ga-rich condition, it might be suppressed the threading dislocation. We believed that out experimental results provide the helpful information to understand and suppressing the defects during the initial growth state. 본 연구에 사용된 GaN 박막은 Ga 증기압을 달리하여 AlN/Si(111) 기판 위에 플라즈마-도움 분자선 켜쌓기 (plasma-assisted molecular beam epitaxy) 법으로 성장되었다. N 과잉 영역에서 성장된 GaN 박막은 거친 표면과 큰 육각형의 결함을 Ga 과잉 영역에서 성장된 시료는 평탄한 표면과 핀홀들이 있는 표면이 관측되었다. 고분해능 X-선 회절기의 흔듦 곡선 측정을 통하여 전파 전위 종류에 따른 선결함 밀도를 측정하였으며, 그 결과 Ga 증기압이 증가할수록 선결함 밀도는 감소하였다. Ga 증기압이 다른 세 시료에 대하여 깊은 결함 과도 분광 (deep level transient spectroscopy)을 측정하였을 때 선결함 (0.46 eV)과 점결함 (0.77 eV)에 관련된 결함 준위들을 관측하였다. 결함 농도를 비교하였을 때 Ga-과잉 영역에서 성장된 GaN 박막의 선결함 밀도는 N 과잉과 N/Ga$\sim$1 영역에서 성장된 시료에 비해 증가율이 매우 적음을 확인하였다. 이는 Ga 과잉 영역에서 초기 성장 시 수평 방향 성장을 빠르게 유도함으로써 기판으로부터 전이되는 결함을 억제할 수 있음을 보여 준다. 이러한 현상의 이해를 통하여 GaN박막 성장 시 결함을 억제하기 위한 초기 성장에 대하여 유용한 정보를 제공할 것으로 보인다.

Fabrication of wide-bandgap β-Cu(In,Ga)₃Se₅ thin films and their application to solar cells

Kim, Ji Hye,Shin, Young Min,Kim, Seung Tae,Kwon, HyukSang,Ahn, Byung Tae Korea Photovoltaic Society 2013 Current Photovoltaic Research Vol.1 No.1

$Cu(In,Ga)_3Se_5$ is a candidate material for the top cell of $Cu(In,Ga)Se_2$ tandem cells. This phase is often found at the surface of the $Cu(In,Ga)Se_2$ film during $Cu(In,Ga)Se_2$ cell fabrication, and plays a positive role in $Cu(In,Ga)Se_2$ cell performance. However, the exact properties of the $Cu(In,Ga)_3Se_5$ film have not been extensively studied yet. In this work, $Cu(In,Ga)_3Se_5$ films were fabricated on Mo-coated soda-lime glass substrates by a three-stage co-evaporation process. The Cu content in the film was controlled by varying the deposition time of each stage. X-ray diffraction and Raman spectroscopy analyses showed that, even though the stoichiometric Cu/(In+Ga) ratio is 0.25, $Cu(In,Ga)_3Se_5$ is easily formed in a wide range of Cu content as long as the Cu/(In+Ga) ratio is held below 0.5. The optical band gap of $Cu_{0.3}(In_{0.65}Ga_{0.35})_3Se_5$ composition was found to be 1.35eV. As the Cu/(In+Ga) ratio was decreased further below 0.5, the grain size became smaller and the band gap increased. Unlike the $Cu(In,Ga)Se_2$ solar cell, an external supply of Na with $Na_2S$ deposition further increased the cell efficiency of the $Cu(In,Ga)_3Se_5$ solar cell, indicating that more Na is necessary, in addition to the Na supply from the soda lime glass, to suppress deep level defects in the $Cu(In,Ga)_3Se_5$ film. The cell efficiency of $CdS/Cu(In,Ga)_3Se_5$ was improved from 8.8 to 11.2% by incorporating Na with $Na_2S$ deposition on the CIGS film. The fill factor was significantly improved by the Na incorporation, due to a decrease of deep-level defects.

Fabrication of wide-bandgap β-Cu(In,Ga)<SUB>3</SUB>Se<SUB>5</SUB> thin films and their application to solar cells

Ji Hye Kim,Young Min Shin,Seung Tae Kim,HyukSang Kwon,Byung Tae Ahn 한국태양광발전학회 2013 Current Photovoltaic Research Vol.1 No.1

Cu(In,Ga)3Se5 is a candidate material for the top cell of Cu(In,Ga)Se2 tandem cells. This phase is often found at the surface of the Cu(In,Ga)Se2 film during Cu(In,Ga)Se2 cell fabrication, and plays a positive role in Cu(In,Ga)Se2 cell performance. However, the exact properties of the Cu(In,Ga)3Se5 film have not been extensively studied yet. In this work, Cu(In,Ga)3Se5 films were fabricated on Mocoated soda-lime glass substrates by a three-stage co-evaporation process. The Cu content in the film was controlled by varying the deposition time of each stage. X-ray diffraction and Raman spectroscopy analyses showed that, even though the stoichiometric Cu/(In+Ga) ratio is 0.25, Cu(In,Ga)3Se5 is easily formed in a wide range of Cu content as long as the Cu/(In+Ga) ratio is held below 0.5. The optical band gap of Cu0.3(In0.65Ga0.35)3Se5 composition was found to be 1.35eV. As the Cu/(In+Ga) ratio was decreased further below 0.5, the grain size became smaller and the band gap increased. Unlike the Cu(In,Ga)Se2 solar cell, an external supply of Na with Na2S deposition further increased the cell efficiency of the Cu(In,Ga)3Se5 solar cell, indicating that more Na is necessary, in addition to the Na supply from the soda lime glass, to suppress deep level defects in the Cu(In,Ga)3Se5 film. The cell efficiency of CdS/Cu(In,Ga)3Se5 was improved from 8.8 to 11.2% by incorporating Na with Na2S deposition on the CIGS film. The fill factor was significantly improved by the Na incorporation, due to a decrease of deep-level defects.

Studies of defect states of ZnO thin films under different annealing conditions

Song, Hooyoung,Kim, Jae-Hoon,Kim, Eun Kyu Elsevier 2009 Microelectronics journal Vol.40 No.2

<P><B>Abstract</B></P><P>ZnO thin films were grown by the pulsed laser deposition technique on <I>c</I>-plane sapphire substrates at a substrate temperature of 500°C with 1×10<SUP>−4</SUP>Torr ambient gas. After the deposition process, ZnO thin films were annealed at 1000°C for 5min under N<SUB>2</SUB> or O<SUB>2</SUB> ambient gas, respectively. In the X-ray patterns, the (002) peak of the annealed sample was shifted from that of the as-grown sample, which indicates a reduced lattice constant of about 1%. Even though the X-ray diffraction patterns in the samples annealed under O<SUB>2</SUB> and N<SUB>2</SUB> annealing gases were almost the same, photoluminescence spectra showed the generation of a shallow level with a few meV, and deep-level states were generated at <I>E</I><SUB>v</SUB>+0.594eV. In addition, a defect state appeared at <I>E</I><SUB>c</SUB>−0.607eV, which originated from hydrogen plasma irradiation on the ZnO sample.</P>

Light Effects of the Amorphous Indium Gallium Zinc Oxide Thin-Film Transistor

이근우,김현재,신현수,김경민,Kon Yi Heo 한국정보디스플레이학회 2009 Journal of information display Vol.10 No.4

The optical and electrical properties of the amorphous indium gallium zinc oxide thin-film transistor (α-IGZO TFT) were studied. When the α-IGZO TFT was illuminated at a wavelength of 660 nm, the off-state drain current slightly increased, while below 550 nm it increased significantly. The α-IGZO TFT wasfound to be extremely sensitive, with deep-level defects at approximately 2.25 eV near the midgap. After UV light illumination, a slight change occurred on the surface of the α-IGZO films, such as in terms of the oxygen 1s spectra, resistivity, and carrier concentrations. It is believed that these results will provide information regarding the photo-induced behaviors in the α-IGZO films.

산소 후열처리에 따른 Ga2O3/SiC photodetector의전기 광학적 특성

정승환,이태희,문수영,박세림,이형진,이건희,구상모 한국전기전자학회 2023 전기전자학회논문지 Vol.27 No.3

본 연구에서는 radio frequency (RF)-스퍼터링을 이용하여 SiC 기판 위에 Ga2O3 박막을 증착하여 Metal-Semiconductor-Metal(MSM) UV photodetector (PD)를 제작하였고, 산소 후열처리에 따른 PD 성능을 연구하였다. 산소 후열처리된 Ga2O3 박막은 외부 광에 대한 전류의 상당한 증가와 시간 의존성 on/off 광 응답 특성에서 측정된 감소시간이 1.21, 1.12 s로 후열처리를 하지 않은 박막의 감소시간인 1.34, 3.01 s 보다 더 빠른 반응을 보여주었다. 이러한 특성은 산소 후열처리 후의 산소 공공 및 결함 분포변화에 기인한다. 우리의 연구 결과는 산소 후열처리가 PD 성능 향상에 영향을 미칠 수 있다는 것을 확인하였다 In this work, we investigated the role of oxygen annealing on the performance of Metal-Semiconductor-Metal(MSM) UV photodetector (PD) fabricated by radio frequency (RF)–sputtered Ga2O3 films on SiC substrates. OxygennnealedGa2O3 films displayed a notable increase in photocurrent and a faster decay time, indicating a decreasein persistent photoconductivity. This improvement is attributed to the reduction of oxygen vacancies and variationof defects by oxygen post-annealing. Our findings provide valuable insights into enhancing PD performance throughoxygen annealing.

Light Effects of the Amorphous Indium Gallium Zinc Oxide Thin-Film Transistor

Lee, Keun-Woo,Shin, Hyun-Soo,Heo, Kon-Yi,Kim, Kyung-Min,Kim, Hyun-Jae The Korean Infomation Display Society 2009 Journal of information display Vol.10 No.4

The optical and electrical properties of the amorphous indium gallium zinc oxide thin-film transistor ($\alpha$-IGZO TFT) were studied. When the $\alpha$-IGZO TFT was illuminated at a wavelength of 660 nm, the off-state drain current slightly increased, while below 550 nm it increased significantly. The $\alpha$-IGZO TFT was found to be extremely sensitive, with deep-level defects at approximately 2.25 eV near the midgap. After UV light illumination, a slight change occurred on the surface of the $\alpha$-IGZO films, such as in terms of the oxygen 1s spectra, resistivity, and carrier concentrations. It is believed that these results will provide information regarding the photo-induced behaviors in the $\alpha$-IGZO films.

Preparation of Intrinsic ZnO Films at Low Temperature Using Oxidation of ZnS Precursor and Characterizion of the Films

Do Hyung Park,Yang Hwi Cho,Dong Hyeop Shin,Byung Tae Ahn 한국태양광발전학회 2013 Current Photovoltaic Research Vol.1 No.2

ZnO film has been used for CIGS solar cells as a buffer layer as itself or by doping Mg and Sn; ZnO film also has been used as a transparent conducting layer by doping Al or B for solar cells. Since ZnO itself is a host material for many applications it is necessary to understand the electrical and optical properties of ZnO film itself with various preparation conditions. We prepared ZnO films by converting ZnS precursor into ZnO film by thermal annealing. ZnO film was formed at low temperature as low as 500°C by annealing a ZnS precursor layer in air. In the air annealing, the electrical resistivity decreased monotonically with increasing annealing temperature; the intensity of the green photoluminescence at 505 nm increased up to 750°C annealing. The electrical resistivity further decreased and the intensity of green emission also increased in reducing atmospheres. The results suggest that deep-level defects originated by oxygen vacancy enhanced green emission, which reduce light transmittance and enhance the recombination of electrons in conduction band and holes in valence. More oxidizing environment is necessary to obtain defect-free ZnO film for higher transparency.