Influence of space charges on the impulse response of InGaAs metal-semiconductor-metal photodetectors

Abstract

Abstruct-The impulse response of interdigitated metalsemiconductor-metal photodetectors fabricated on an Fe-doped InGaAs absorbing layer and an Fe-doped InP barrier enhancement layer is investigated. For ultra-short pulse excitation of 150 fs at .h = G 2 0 nm the photoresponse is found to be less than 13 ps FWHM for detectors with 1 pm finger spacing. Above a certain level of illumination, the peak amplitude increases sublinearly and the relative contribution of the tail to the detector response is appreciably enhanced. The screening of the electric field by photo-generated space charges is responsible for this nonlinearity. For detectors with 5 pm finger spacing illuminated with 1.3 pm light pulses (FWHM = 33 ps), space charge perturbation of the impulse response manifests itself by a decrease of the FWHM and an increase of the fall time with increasing illumination level. The practical consequences for the performance of MSM detectors in various applications are discussed.

Microwave Optical Switches Metal–Semiconductor–Metal Schottky based on GaAs

“…Near the anode, in the low field region electron-hole plasma is formed, this region contains more holes than electrons, where they move at much lower velocities [6,10,12,13,14]. When substrate is deeper, these carriers are collected at much lower speeds [11], it explained as follows: inside the space-charge region, a strong field accelerates electrons towards the bulk just beyond this region, a retarding filed sweeps the electrons toward the surface [15], this leads to increase fall time.…”

“…The increase of FWHM and fall time of pulse response with increasing optical power is explained as follows. The pulse energy is high enough to cause accumulation in the active region, screening of internal electric field, and formed an electron hole plasma near the anode, this region behave like virtual anode because a lot of holes are still staying in this region [6,13]. The transient current response is limited by another factor, the trapping at the surface states of semiconductor states carriers create surface charge layer, [15,19], also, at active layer metal-semiconductor interface and/or at deep layer defects in band gab of the material can trap photgenerated carriers [10,12,13,20,21,22].…”

“…We can neglect the screening of the internal electric field to have no effect on the MSM photoswitch response if the space charges are much less than the total charge accumulated at the contacts [13,22,23]. If each photon creates one electron-hole pair, the total number of the photogenerated carriers with total area L2 [6,13]:…”

“…If each photon creates one electron-hole pair, the total number of the photogenerated carriers with total area L2 [6,13]:…”

Design considerations for high-current photodetectors

“…This point is particularly important in optically steered phased array antennas since any increase in photodetector output signal level reduces the necessary phase-and amplitude-matched electronic gain at each antenna element. In an effort to increase the output photocurrent, a number of groups have been studying surface-illuminated [6]- [11], metal-semiconductor-metal [12], [13], waveguide [14], [15], traveling-wave [16], [17], and photodetector arrays [18], [19]. The ability to increase photocurrent depends on two primary factors: 1) space-charge limitations which are influenced by physical dimensions, structure type, illumination conditions, maximum electric field, etc.…”