Homojunction Photodiodes Research Articles

Impact of CdTe/CdZnTe substrate resistivity on performance degradation of long-wavelength n/sup +/-on-p HgCdTe infrared photodiodes

For realizing HgCdTe focal plane arrays on alternate substrates (Si or GaAs), CdTe buffer layers are essential. Bulk CdTe/CdZnTe substrates are also used for LPE growth of HgCdTe. A model for the effect of the n-CdTe substrate resistivity on the quantum efficiency, /spl eta/, and the dynamic resistance-area product, R/sub d/A, of a n/sup +/-on-p HgCdTe backside illuminated photodiode has been developed, taking into account the effect of the graded heterointerface between CdTe/CdZnTe and HgCdTe on the homojunction photodiode. The issue of how low the substrate/buffer layer resistivity can be, without degrading the performance of the photodiode, has been addressed. For low substrate resistivities, the R/sub d/A can drop by about 50%, while the quantum efficiency decreases by about 5%. It has been found that as low as 2 /spl Omega/-cm for long wavelength IR photodiodes (cutoff wavelength 14 /spl mu/m) is acceptable. To obtain the R/sub d/A and /spl eta/ from the band profile, a linear approximation has been used in which the interface barrier region has a constant electric field, while the bulk of the epilayer has no electric field. General expressions have been derived for the R/sub d/A and /spl eta/ in this two-region model. Our solutions are valid for both high and low electric fields, unlike previously derived solutions in the literature valid either in the one-region low-field case or the two-region, high-field approximation.

Spectral response of a photodiode using 3C-SiC single crystalline film

Abstract 3C-SiC/Si heterojunction photodiodes and 3C-SiC homojunction photodiodes have been fabricated by atmospheric chemical vapor deposition. The maximum quantum efficiency of heterojunction photodiodes with a window layer of 10 μm thick is 80% at 550 nm. An increase in the thickness of the SiC layer reduces the responsivity in wavelength regions shorter and longer than 500–550 nm. 3C-SiC self supported films of 20 μm thick, epitaxially grown on Si, have been used as substrates for homojunction photodiodes. The responsivity of the homojunction photodiode with a window layer thickness of 0.5 μm is 72 mA/W at 250 nm with a quantum efficiency of 36%. When the thickness of the window layer is decreased, the peak responsivity increases and the peak wavelength shifts to a shorter wavelength. These spectral responsivities are discussed together with the results of calculations using a one-dimensional model.

InGaSb/GaSb photodiodes grown by MOVPE

We report a systematic investigation of the growth by MOVPE of a series of InGaSb photodiodes lattice-mismatched on GaSb substrates. The samples were grown in two atmospheric pressure MOVPE reactors and with different organometallic sources. We have investigated the use of various intermediate layers between the substrate and the homojunction photodiode such as compositional ramps, steps and superlattices in order to prevent dislocations due to the lattice mismatch from reaching the crucial p/n junction at the top of the device. The top layers have been evaluated by X ray diffraction, SIMS profiling and imaging, Hall and resistivity measurements. From these layers, photodiodes were fabricated with mesa wet etching without any antireflecting coating. Electrical and optical characteristics of these photodiodes — dark current, capacitance and external quantum efficiency — were investigated at room temperature. The dark current and diffusion length are compared with a p/n InGaSb homojunction grown without intermediate layer and with a p/n InGaAsSb homojunction lattice-matched on GaSb.

2.6 μm InGaAs photodiodes

We have developed In0.82Ga0.18As p-n homojunction photodiodes that have a long-wavelength threshold at about 2.65 μm. A compositionally graded InxGa1−xAs layer accommodates the 2% lattice mismatch between the InP substrate and the In0.82Ga0.18As active layers of the device. At −2 V reverse bias the room-temperature dark current is 3.5 μA (32 mA/cm2), and the quantum efficiency is 70–75% over the wavelength interval of 2.1–2.6 μm.

Detectivity calculations of III–V ternary compound PDB photodetectors

The spectral specific detectivities of some III V ternary compound planar doped barrier (PDB) photodetectors have been calculated in this paper. The calculated detectivity of a Ga 0.47In 0.53As PDB photodetector has also been compared with that of an abrupt p 4 n homo-junction photodiode, and the relative merits of the former structure are discussed.

The Ga0.47In0.53As homojunction photodiode—A new avalanche photodetector in the near infrared between 1.0 and 1.6 μm

A new p-n photodetector operating at room temperature and sensitive in the near infrared for wavelengths as long as 1.6 μm has been made from Ga0.47In0.53As grown lattice matched on InP substrates by LPE. These detectors display avalanche gain and dark current as low as 2×10−9 A. Measurements of the speed of response at 1.06 μm have shown a detector response time as fast as 250 psec.