Sehun Park

Study of Multi-stacked InAs Quantum Dot Infrared Photodetectors Grown by Metal Organic Chemical Vapor Deposition

We grew multi-stacked InAs/ DWELL (dot-in-a-well) structure by metal organic chemical vapor deposition and investigated optical properties by photoluminescence and I-V characteristics by dark current measurement. When stacking InAs quantum dots (QDs) with same growth parameter, the size and density of QDs were changed, resulting in the bimodal emission peak. By decreasing the flow rate of TMIn, we achieved the uniform multi-stacked QD structure which had the single emission peak and high PL intensity. As the growth temperature of n-type GaAs top contact layer (TCL) is above , the PL intensity severely decreased and dark current level increased. At bias of 0.5 V, the activation energy for temperature dependence of dark current decreased from 106 meV to 48 meV with increasing the growth temperature of n-type GaAs TCL from 580 to . This suggest that the thermal escape of bounded electrons and non-radiative transition become dominant due to the thermal inter-diffusion at the interface between InAs QDs and well layer.

Growth of GaN Layer on Patterned Al/Ti Metal Mask by Metal-Organic Chemical Vapor Deposition

We report on high-quality GaN epitaxial growth by metal–organic chemical vapor deposition (MOCVD) on a stripe-patterned GaN template using a metal mask. A multiple Al/Ti metal system with 10 µm periodicity was used as a masking layer for the epitaxial lateral overgrowth (ELOG). The overgrowth of GaN on the patterned metal mask begins at the open window region between the stripes, and then ELOG leads to the formation of a continuous layer. Micro-cathodoluminescence (µ-CL) results show the improvement of optical properties and significant strain relaxation in the overgrown GaN layer. About a 2-order reduction of threading dislocation density was observed on the overgrown GaN on metal mask regions compared with that on GaN template regions.

Multi-step plasma etching process for development of highly photosensitive InSb mid-IR FPAs

Reactive ion beam etching (RIBE) with CH4/H2/Ar or Cl2/Ar and ion beam etching (IBE) with Ar has been widely used for indium-contained compound semiconductors such as InAs, InP and InSb. To improve the performance of InSb FPAs, reduction of the ion-induced defects and the surface roughness is one of the key issues. To find the optimized plasma etching method for the fabrication of InSb devices, conventional plasma etching processes were comparatively investigated. RIBE of InSb was observed to generate residual by-products such as carbide and chloride causing the degradation of devices. On the other hand, very smooth surface was obtained by etching with N2. However, the etch rate of the N2 etching was too slow for the application to the device fabrication. As an alternative way to solve these problems, a multi-step plasma etching process, a combination of the Ar etching and the N2 etching, for InSb was developed. As gradually increasing the amount of N2 gas flow during the etching process, the plasma damage causing the surface roughen decreased and consequently smoother surface close to that of N2 RIE could be obtained. Furthermore, Raman analysis of the InSb surface after the plasma etching indicated clearly that the multi-step etching process was an effective approach in reducing the ion-induced damages on the surface.

Suppression of surface leakage current in InSb photodiode by ZnS passivation

We have investigated the suppression of surface leakage current in InSb photodiodes using ZnS passivation. Capacitance-voltage characteristics for metal-insulator-semiconductor (MIS) devices showed that positive fixed charges were introduced in the ZnS film and they compensated the negative fixed charges in InSb. AES and PL analysis revealed that the ZnS films were S-deficient and the positive fixed charges were originated from the sulphur vacancy. An InSb pn photodiode structures passivated with ZnS film deposited at 1.5 A/s showed the lowest surface leakage current, which is consistent with the result that it was close to the ideal flat-band condition. This indicates that deposition of S-deficient ZnS film is an effective way to suppress the dark current in InSb photodiode.

Enhancement of Interface Properties between Passivation Layers and InSb by Using Remote PECVD

We report the enhanced interface properties between passivation layers and InSb by using remote PECVD system. SiO2 and Si3N4 layers deposited by remote PECVD showed lower interface trap densities than layers deposited by normal PECVD. SiO2 layers deposited by remote PECVD showed 7.1×1011 cm−2 eV−1 of interface trap density at midgap which is slightly lower than SiO2 layers deposited by PECVD. Si3N4 layers deposited by remote PECVD showed 1.6∼1.7×1012 cm−2 eV−1 at midgap which is 3 times lower than Si3N4 layers deposited by PECVD. Interface properties of SiO2 are superior to that of Si3N4 in both case of PECVD and remote PECVD. To investigate the interface properties between SiO2 and InSb, X‐ray photoelectron spectroscopy was conducted. Indium and antimony oxide phases were found at the interface and these oxide phases could act as the origin of interface traps.

Effect of drain bias stress on the stability of nanocrystalline silicon thin film transistor with various channel length

Nanocrystalline silicon (nc-Si) thin film transistor (TFT) has attracted considerable attention for various applications such as display and image sensor [1]. It can be fabricated with rather simple process as compared with polycrystalline silicon (poly-Si) TFT since it doesn’t require additional recrystallization process. It also exhibits better uniformity while recrystallization process causes troublesome nonuniformity problem in poly-Si TFT [2,3]. nc-Si TFT also has advantage compared to hydrogenated amorphous silicon (a-Si:H) TFT due to better electrical stability [4].