J. W. Choe

Short-wavelength infrared photodetector on Si employing strain-induced growth of very tall InAs nanowire arrays

One-dimensional crystal growth enables the epitaxial integration of III-V compound semiconductors onto a silicon (Si) substrate despite significant lattice mismatch. Here, we report a short-wavelength infrared (SWIR, 1.4–3 μm) photodetector that employs InAs nanowires (NWs) grown on Si. The wafer-scale epitaxial InAs NWs form on the Si substrate without a metal catalyst or pattern assistance; thus, the growth is free of metal-atom-induced contaminations, and is also cost-effective. InAs NW arrays with an average height of 50 μm provide excellent anti-reflective and light trapping properties over a wide wavelength range. The photodetector exhibits a peak detectivity of 1.9 × 108  cm·Hz1/2/W for the SWIR band at 77 K and operates at temperatures as high as 220 K. The SWIR photodetector on the Si platform demonstrated in this study is promising for future low-cost optical sensors and Si photonics.

Reduction of Light Reflectance from InAlP by the Texture Formation Using Ultra-Thin Pt Layer

Textured surface has been fabricated to reduce the light reflectance from the solar cells. The textured surface is very suitable for the multi-junction III-V solar cells because it can decrease the light reflectance over a large wavelength range. In this study, we have generated a textured structure on InAlP which is used for the window layer of the multi-junction III-V solar cells. Ultra-thin Pt layer (0.7 nm) has been used for wet etching mask. An array of nanosized pyramid shape formed on InAlP surface dramatically reduces the light reflectance up to 13.7% over a large wavelength range (i.e., ).태양전지의 표면에 텍스쳐 구조를 형성하면 빛의 반사율을 줄일 수 있으므로 태양전지의 효율을 증가시킬 수 있다. 또한 표면의 텍스쳐 구조는 넓은 파장대역에서 빛의 반사를 줄여주기 때문에 다중접합 III-V화합물 태양전지에 아주 유용하다. 본 연구에서는 얇은 Pt층을 식각 마스크로 사용하여 다중접합 III-V태양전지의 window층으로 사용되는 InAlP층에 다양한 텍스쳐 구조를 형성하고 반사율을 측정하였다. 습식식각에 의해 나노미터 크기로 형성된 피라미드 꼴 텍스쳐 구조는 0.3∼1.5 μm의 넓은 파장영역에서 빛의 반사율을 13.7%까지 감소시켰다.

Single Crystalline In x Ga 1-x As Nanowires on Si (111) via VLS Method

Single crystalline nanowires are grown on Si (111) substrate via Vapor-Liquid-Solid growth mode using metal-organic chemical vapor deposition. The ternary nanowires have been grown with various growth conditions and examined by electron microscopy. The alloy compositions of the nanowires has been investigated using Energy-dispersive X-ray spectroscopy. We have found that the composition gradient of the nanowire becomes larger with growth temperature and V/III ratio.