Novel black silicon PIN photodiodes

Abstract

The many advantages of silicon such as low cost, abundancy and a level of maturity that allows for very large scale integration, means that silicon is the most commonly used semiconductor in microelectronics and optoelectronic devices. Silicon, however, has one disadvantage, this being that it is unable to absorb light greater than 1100 nm. The two primary telecommunications wavelengths, 1300 nm and 1550 nm, can therefore not be detected. An interesting method used to extend silicon's wavelength range is the formation of black silicon on the silicon surface. Black silicon is formed when gases that are passed over the silicon react and etch the silicon surface, forming a dark spiky pattern. When light is shone on such a pattern, it repeatedly bounces back and forth between the spikes thus reducing surface reflection and trapping the light. This reduced reflectance and light trapping increases the sensitivity of the silicon to long wavelengths and makes it viable for use in a wide range of commercial devices such as infrared detectors and solar cells. This paper presents novel black silicon PIN photodiodes of various sizes (25 mm 2 , 4 mm 2 and 1 mm 2 ). The diodes have been extensively characterized at wafer level, with breakdown voltage, dark current, shunt resistance, threshold voltage and junction capacitance measurements being made. Extensive responsivity measurements were also performed and it was established that the black silicon surface resulted in responsivity increases of greater than 50 % at long wavelengths (≃ 1100 nm).