• Current Photovoltaic Research
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• v.8 no.3
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• pp.102-106
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• 2020

In this paper, the effect of MoSe₂ on the contact resistance (R_C) of the transparent conducting oxide (TCO) and Mo junction in the scribed P2 region of the Cu(In,Ga)Se₂ (CIGS) solar module was analyzed. The CIGS/Mo junction becomes ohmic-contact by MoSe₂, so the formation of the MoSe₂ layer is essential. However, the CIGS solar module has a TCO/MoSe₂/Mo junction in the P2 region due to structural differences from the cell. The contact resistance (R_C) of the P2 region was calculated using the transmission line method, and MoSe₂ was confirmed to increase R_C of the TCO/Mo junction. B doped ZnO (BZO) was used as TCO, and when BZO/MoSe₂ junction was formed, conduction band offset (CBO) of 0.6 eV was generated due to the difference in their electron affinities. It is expected that this CBO acts as a carrier transport barrier that disturbs the flow of current, resulting in increased R_C. In order to reduce the R_C caused by CBO, MoSe₂ must be made thin in a CIGS solar module.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.72-72
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• 2011

Recently, Zinc oxide (ZnO) nano-structures have been received attractive attention because of their outstanding optical and electrical properties. It might be a promising material considered for applications to photonic and electronic devices such as ultraviolet light emitting diode, thin film transistor, and gas sensors. ZnO nano-structures can be typically synthesized by the VLS growth mode and self-assembly. In the VLS growth mode using various growth techniques, the noble metal catalysts such as Au and Sn were used. However, the growth of ZnO nano-structures on nano-crystalline Au seeds using radio frequency (RF) magnetron sputtering might be explained by the profile coating, i.e. the ZnO nano-structures were a morphological replica of Au seeds. Ga doped ZnO (ZnO:Ga) nano-structures using this concept were synthesized and characterized by XRD, AFM, SEM, and TEM. We found that surface morphology is drastically changed from initial islands to later sun-flower typed nano-structures. We will present the structural evolution of ZnO:Ga nano-structures with increasing the film thickness.

• Journal of the Korean institute of surface engineering
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• v.29 no.5
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• pp.325-329
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• 1996

We report on p-type arsenic doping of metalorganic vapor phase epitaxially (MOVPE) grown HgCdTe on (100) GaAs. HgCdTe was grown at $370^{\circ}C$ in a horizontal reactor with using dimethy-cadmium, diisoprophyltelluride, and elemental Hg. We used tris-dimethylaminoarsenic (DMAAs) as the metalorganic for p-doping. 4micron thick CdTe and subsequently 10micron thick HgCdTe were grown on (100) GaAs substrate. Interdiffused multilayer process in which thin CdTe and HgTe layers are grown alternately and interdiffused to obtain homogeneous HgCdTe alloys was used. Arsenic was doped during CdTe growth cycle. After growth HgCdTe was annealed at $415^{\circ}C$ for 15 min and then annealed again at $220^{\circ}C$ for 3 hr, both with Hg-saturate condition. We could obtain p-doping from 2.5$\times$$10^{16}$ to 6.6$\times$$10^{17}$$cm^{-3}$, depending on the DMAAs partial pressure. With the dual Hg-annealing, activation of arsenic was aboutt 90%, which was confirmed by SIMS measurement. With only low temperature annealing at $220^{\circ}C$ for 3hr, activation efficiency was about 50%.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.23-27
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• 2008

We have investigated the effect of annealing on the structural and optical properties of polycrystalline Ga doped ZnO (GZO) films grown on glass substrates by RF-magnetron sputter at room temperature. The structural and optical properties of as-grown GZO films were characterized and then samples were annealed at $400{\sim}600^{\circ}C$ in $N_2$ ambient for 30, 60 minutes, respectively. The field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to measure the grain size and the crystalline quality of the films. We found that the crystalline quality was improved and the grain size tends to be increased. The optical properties of GZO thin films were analyzed by UV-VIS-NIR spectrophotometers. It is found that optical properties of thin films are increased by annealing and can be used for transparent electrode application. We believe that the appropriate post-growth heat treatment could be contributed to the improvement of GZO-based devices.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.1012-1017
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• 1999

Low resistance ohmic contacts to the Si-doped $\textrm{In}_{0.17}\textrm{Ga}_{0.83}\textrm{N}$(~$\times10^{19}\textrm{cm}^{-3}$) were obtained using the W metallization schemes. Specific contact resistance decreased with increasing annealing temperature. The lowest resistance is obtained after a nitrogen ambient annealing at $950^{\circ}C$ for 90 s, which results in a specific contact resistance of $2.75\times10^{-8}\Omega\textrm{cm}^{-3}$. Interfacial reactions and surface are analyzed using x-ray diffraction and scanning electron microscopy (SEM). The X-ray diffraction results show that the reactions between the W film and the $\textrm{In}_{0.17}\textrm{Ga}_{0.83}\textrm{N}$ produce a $\beta$-$W_2N$ phase at the interface. The SEM result shows that the morphology of the contacts is stable up to a temperature as high as $850^{\circ}C$. Possible mechanisms are proposed to describe the annealing temperature dependence of the specific contact resistance.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.334-334
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• 2012

Transparent oxide semiconductors have recently attracted much attention as channel layer materials due to advantageous electrical and optical characteristics such as high mobility, high stability, and good transparency. In addition, transparent oxide semiconductor can be fabricated at low temperature with a low production cost and it permits highly uniform devices such as large area displays. A variety of thin film transistors (TFTs) have been studied including ZnO, InZnO, and InGaZnO as the channel layer. Recently, there are many studies for substitution of Ga in InGaZnO TFTs due to their problem, such as stability of devices. In this work, new quaternary compound materials, tantalum-indium-tin oxide (TaInSnO) thin films were fabricated by using co-sputtering and used for the active channel layer in thin film transistors (TFTs). We deposited TaInSnO films in a mixed gas (O2+Ar) atmosphere by co-sputtering from Ta and ITO targets, respectively. The electric characteristics of TaInSnO TFTs and thin films were investigated according to the RF power applied to the $Ta_2O_5$ target. The addition of Ta elements could suppress the formation of oxygen vacancies because of the stronger oxidation tendency of Ta relative to that of In or Sn. Therefore the free carrier density decreased with increasing RF power of $Ta_2O_5$ in TaInSnO thin film. The optimized characteristics of TaInSnO TFT showed an on/off current ratio of $1.4{\times}108$, a threshold voltage of 2.91 V, a field-effect mobility of 2.37 cm2/Vs, and a subthreshold swing of 0.48 V/dec.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.327-327
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• 2009

ZnO with a large band gap (~3.37 eV) and exciton binding energy (~60 meV), is suitable for optoelectronic applications such as ultraviolet (UV) light emitting diodes (LEDs) and detectors. However, the ZnO-based p-n homojunction is not readily available because it is difficult to fabricate reproducible p-type ZnO with high hall concentration and mobility. In order to solve this problem, there have been numerous attempts to develop p-n heterojunction LEDs with ZnO as the n-type layer. The n-ZnO/p-GaN heterostructure is a good candidate for ZnO-based heterojunction LEDs because of their similar physical properties and the reproducible availability of p-type GaN. Especially, the reduced lattice mismatch (~1.8 %) and similar crystal structure result in the advantage of acquiring high performance LED devices. In particular, a number of ZnO films show UV band-edge emission with visible deep-level emission, which is originated from point defects such as oxygen vacancy, oxygen interstitial, zinc interstitial[1]. Thus, defect-related peak positions can be controlled by variation of growth or annealing conditions. In this work, the undoped ZnO film was grown on the p-GaN:Mg film using RF magnetron sputtering method. The undoped ZnO/p-GaN:Mg heterojunctions were annealed in a horizontal tube furnace. The annealing process was performed at $800^{\circ}C$ during 30 to 90 min in air ambient to observe the variation of the defect states in the ZnO film. Photoluminescence measurements were performed in order to confirm the deep-level position of the ZnO film. As a result, the deep-level emission showed orange-red color in the as-deposited film, while the defect-related peak positions of annealed films were shifted to greenish side as increasing annealing time. Furthermore, the electrical resistivity of the ZnO film was decreased after annealing process. The I-V characteristic of the LEDs showed nonlinear and rectifying behavior. The room-temperature electroluminescence (EL) was observed under forward bias. The EL showed a weak white and strong yellowish emission colors (~575 nm) in the undoped ZnO/p-GaN:Mg heterojunctions before and after annealing process, respectively.

• Korean Journal of Materials Research
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• v.28 no.11
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• pp.659-662
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• 2018

We report the properties of infrared photodetectors based on two kinds of quantum dots(QDs): i) 2.0 ML InAs QDs by the Stranski-Krastanov growth mode(SK QDs) and ii) sub-monolayer QDs by $4{\times}[0.3ML/1nm\;In_{0.15}Ga_{0.85}As]$ deposition(SML QDs). The QD infrared photodetector(QDIP) structure of $n^+-n^-(QDs)-n^+$ is epitaxially grown on GaAs (100) wafers using molecular-beam epitaxy. Both the bottom and top contact GaAs layers are Si doped at $2{\times}10^{18}/cm^3$. The QD layers are grown with Si doping of $2{\times}10^{17}/cm^3$ and capped by an $In_{0.15}Ga_{0.85}As$ layer at $495^{\circ}C$. The photoluminescence peak(1.24 eV) of the SML QDIP is blue-shifted with respect to that (1.04 eV) of SK QDIPs, suggesting that the electron ground state of SML QDIP is higher than that of the SK QDIP. As a result, the photoresponse regime(${\sim}9-14{\mu}m$) of the SML QDIP is longer than that (${\sim}6-12{\mu}m$) of the SK QDIP. The dark current of the SML QDIP is two orders of magnitude smaller value than that of the SK QDIP because of the inserted $Al_{0.08}Ga_{0.92}As$ layer.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.135-135
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• 2010

In Mn-Ge equilibrium phase diagram, many Mn-Ge intermetallic phases can be formed with difference structures and magnetic properties. The MnGe has the cubic structure and antiferromagnetic(AFM) with Neel temperature of 197 K. The calculation predicted that the $MnGe_2$ with $Al_2Cu$-type is hard to separate between the paramagnetic(PM) states and the AFM states because this compound displays PM and AFM configuration swith similar energy. Mn-doped Ge showed the FM with Currie temperature of 285 K for bulk samples and 116 K for thin films. In addition, the $Mn_5Ge_3$ compound has hexagonal structure and FM with Curie temperature around 296K. The $Mn_{11}Ge_8$ compound has the orthorhombic structure and Tc is low at 274 K and spin flopping transition is near to 140 K. While the bulk $Mn_3Ge_2$ exhibited tetragonal structure ($a=5.745{\AA}$;$c=13.89{\AA}$) with the FM near to 300K and AFM below 150K. However, amorphous $Mn_3Ge_2$ ($a-Mn_3Ge_2$) was reported to show spin glass behavior with spin-glass transition temperature (Tg) of 53 K. In addition, the transition of crystalline $Mn_3Ge_2$ shifts under high pressure. At the atmospheric pressure, $Mn_3Ge_2$ undergoes the magnetic phase transition from AFM to FM at 158 K. The pressure dependence of the phase transition in $Mn_3Ge_2$ has been determined up to 1 GPa. The transition was found to occur at 1 GPa and 155 K with dT/dP=-0.3K/0.1 GPa. Here report that Ferromagnetic $Mn_3Ge_2$ thin films were successfully grown on GaAs(001) and GaSb(001) substrates using molecular beam epitaxy. Our result revealed that the substrate facilitates to modify magnetic and electrical properties due to tensile/compressive strain effect. The spin-flopping transition around 145 K remained for samples grown on GaSb(001) while it completely disappeared for samples grown on GaAs(001). The antiferromagnetism below 145K changed to ferromagnetism and remained upto 327K. The saturation magnetization was found to be 1.32 and $0.23\;{\mu}B/Mn$ at 5 K for samples grown on GaAs(001) and GaSb(001), respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.145-146
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• 2006

The most Important research topic in the development of ZnO LED and LD is the production of p-type ZnO thin film that has minimal stress with outstanding stoichiometric ratio. In this study, Phosphorus diffused into the undoped ZnO thin films using the ampoule-tube method for the production of p-type znO thin films. The undoped ZnO thin films were deposited by RF magnetron sputtering system on $GaAs_{0.6}P_{0.4}$/GaP and Si wafers. 4N Phosphorus (P) was diffused into the undoped ZnO thin films in ampoule-tube which was performed and $630^{\circ}C$ during 3hr. We found the diffusion condition of the conductive ZnO films which had p-type properties with the highest mobility of above 532 $cm^2$/Vs compared with other studies PL spectra measured at 10K for the purpose of analyzing optical properties of p-type ZnO thin film showed strong PL intensity in the UV emission band around 365nm ~ 415nm and 365nm ~ 385nm.