Photodiodes comprise a plurality of electrode radiation-sensitive junctions formed in semiconductor material. Within a photodiode, charge carriers are created by light that illuminates the junction and photo current is generated dependent upon the degree of illumination. Photodiodes are used for detection of optical power and subsequent conversion of the same to electrical power. Operationally, photodiodes absorb photons and charged particles, which facilitate detection of incident optical power, thereby generating current proportional to the incident power.
Photodiodes are typified by the quantification of certain characteristics, such as electrical, optical, current (I), voltage (V), and noise. Electrical characteristics predominantly include shunt resistance, series resistance, junction capacitance, rise or fall time and frequency response whereas optical characteristics include responsivity, quantum efficiency, non-uniformity, and non-linearity. Noise in photodiodes is generated by a plurality of sources including, but not limited to, thermal noise, quantum or photon or shot noise, and flicker noise.
In the semiconductor industry it is often desirable to increase light-induced current of photodiodes in order to increase the signal-to-noise ratio and thereby enhance photodiode sensitivity. Photodiode sensitivity is crucial in low light-level applications and is typically quantified by noise equivalent power (NEP) defined as the optical power that produces a signal-to-noise ratio of unity at the detector output. NEP is usually specified at a given wavelength and over a frequency bandwidth of 1 Hz and is therefore expressed in units of W/Hz1/2.
Silicon photodiodes, essentially active solid-state semiconductor devices, are among the most popular photodetectors providing high performance over a wide wavelength range. For example, silicon photodiodes are sensitive to light in the wide spectral range, approximately 200*10−9 m to 1200*10−9 m, extending from deep ultraviolet all the way through visible to near infrared. Additionally, silicon photodiodes detect the presence or absence of minute light intensities thereby facilitating precise measurement of the same on appropriate calibration. For instance, appropriately calibrated silicon photodiodes detect and measure light intensities varying over a wide range, from very minute light intensities of below 10−13 watts/cm2 to high intensities above 10−3 watts/cm2.
Silicon photodiodes can be employed in an assortment of applications including, but not limited to, spectroscopy, distance and speed measurement, laser ranging, laser guided missiles, laser alignment and control systems, optical free air communication, optical radar, radiation detection, optical position encoding, film processing, flame monitoring, scintillator read out, environmental applications such as spectral monitoring of earth ozone layer and pollution monitoring, low light-level imaging, such as night photography, nuclear medical imaging, photon medical imaging, and multi-slice computer tomography (CT) imaging, security screening and threat detection, thin photochip applications, and a wide range of computing applications.
Several problems exist with conventional photodiodes currently in use. In particular, for relatively short wavelength illumination, for instance below 800 nm, edge-illuminated silicon photodiodes absorb light very strongly near the edge surfaces thereby leading to low responsivity due to edge surface recombination. Likewise, controlling quantum efficiency, specifically in case of edge illuminated InGaAs/InP photodiodes, still remains a challenge.
The prior art fails to describe edge illuminated photodiodes that provide for lesser susceptibility to surface recombination effects, and possess high responsivity, and high quantum efficiency respectively. Consequently, there is still a need for photodiodes possessing high responsivity and high quantum efficiency. More specifically, there is demand for high responsivity edge illuminated silicon photodiodes having lesser susceptibility to surface recombination effects, which in turn is accountable for minimization of responsivity. Furthermore, high quantum efficiency edge illuminated InGaAs/InP photodiodes are also still needed.