SWIR (Short-wave Infrared) image sensors based on the InGaAs PIN photo-diode arrays present a tremendous interest in applications such as surveillance and reconnaissance systems. The InGaAs SWIR PIN detectors have a photo response in the $0.9~1.7 \mu m$ wavelength range coinciding with peaks in the ambient night glow, which is an effective illumination source for passive low light level imaging [1]. Pla-nar- and mesa-type device structures are commonly used in InGaAs/InP PIN photo-detectors. The planar-type PIN photodetectors are widely utilized due to the low dark current characteristic which is the key parameter required in the high performance SWIR PIN photodetectors. On the other hand, the mesa-type PIN photodetectors are actively researched because of their potential advantages of achieving the more min-iature size and low crosstalk which is the key performance for imaging applications.
In this thesis, the mesa-type InGaAs/InP PIN photodiodes with low dark cur-rent characteristics has been fabricated and characterized. The fabrication steps for the mesa-type PIN photodiodes are as follows. Firstly, a circular-type mesa structure was realized by the optimized etching technique which is the HBr-based dry- and wet-etch process, and then passivated using the $SiO_2$ film. On the p-doped areas of InGaAs photodiodes, a p-contact was formed by a optimized metal layer of Zn/Au/Cr/Au which has a specific contact resistivity of $6.05 \times 10^{-5} \Omega \cdot cm^2$, then followed by a post-metallization annealing process. Finally, the fabricated mesa-type In-GaAs/InP PIN photodiodes have shown a $R_0A$ of $1.2 \times 10^3 \Omega \cdot cm^2$ and a low dark cur-rent density of $3.2 \mu A/cm^2$ which is equal to the value of world best mesa-type dark current characteristic.
Next, the effects of thermal treatments with different time duration and tem-perature for the mesa-type InGaAs/InP PIN photodetectors are investigated and ana-lyzed to improve the dark current characteristics. In order to obtain the optimal con-dition of thermal treatment, various types of mesa-type photodiodes with different time duration have been developed. From the measured results, the optimum time duration is 1 minute and temperature is $500^\circ C$ in this work. The fabricated mesa-type PIN photodiode with the thermal treatment for 1 minute at $500^\circ C$ shows a $R_0A$ of $2.19 \times 10^4 \Omega \cdot cm^2$ and a lowest dark current density of $803 nA/cm^2$, which is the best value in this work. The responsivity of the fabricated mesa-type PIN photodiode with thermal treatment for 1 minute at $500^\circ C$ is measured to be 0.78 A/W for a 1550 nm light source. The related quantum efficiency is calculated to be 62 %.
Consequently, the result of the mesa-type InGaAs/InP PIN photodiodes with an optimal condition of the thermal treatment is formed to be very promising for SWIR imaging applications.
SWIR 대역을 이용한 이미지 센서는 $0.9~1.7 \mu m$ 대역의 파장을 흡수하며 빛이 없는 밤에 존재하는 night glow를 검출하는 등 다양한 장점으로 인해 군수 뿐만 아니라 민수용으로도 각광을 받고 있다. 이러한 SWIR 대역을 이용한 이미지 센서의 대표적인 구조는 평면형과 메사형 구조가 있다. 평면형의 경우 암전류 특성이 좋다라는 이유로 굉장히 활발히 연구되고 있는 구조이며, 메사형의 경우 작은 사이즈 생산 가능성과 crosstalk 성능이 좋다라는 이유로 최근 많은 연구가 진행되고 있는 구조이다.
이번 연구에서는 암전류 특성이 좋은 메사형 InGaAs/InP PIN photodiode를 제작하였다. 공정 순서는 먼저 원형의 메사형 구조를 가지는 소자를 에칭을 통해 활성영역을 만든다. 그리고는 표면 전반에 보호막을 형성하고 p-type InP에 ohmic contact을 형성하기 위해 Zn/Au/Cr/Au를 증착한다. 이렇게 증착된 ohmic contact metal의 specific contact resistivity는 $6.05 \times 10^{-5} \Omega \cdot cm^2$ 값을 가진다. 이를 통해 제작된 소자의 $R_0A$ 는 $1.2 \times 10^3 \Omega·\cdot cm^2$ 이며, 암전류는 $3.2 \mu A/cm^2$ 으로서 현재 보고되고 있는 메사형 최고 암전류 특성과 동일한 값이다.
