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Heterostructure Optoelectronic Devices
Published in Vinod Kumar Khanna, Introductory Nanoelectronics, 2020
There are two possibilities. One possibility is that the electron-hole pairs created in the well recombine. Then they do not contribute to the short circuit current of the cell; instead the open circuit voltage is diminished. The other possibility is that the generated charge carriers escape from the well and take part in photocurrent production. This is achieved by making the barriers thin enough so that the carriers escape from the well by tunneling through the barrier with the help of thermal energy at room temperature (Ekins-Daukes et al. 2009). Thus the cell must be designed in such a way that the two competing and counteracting mechanisms of carrier recombination and thermally assisted tunneling take place at the appropriate rates for the successful operation of the cell. The wells are usually 2–5 nm thick and the barrier thickness is generally 10 nm or less. To prevent carrier loss by recombination, the minority-carrier lifetime in the semiconductor material must be long. It is determined by the quality of the material and absence of defects.
Photonic Devices
Published in John D. Cressler, H. Alan Mantooth, Extreme Environment Electronics, 2017
Typically, the semiconductor material quality is high so that there is at least an order of magnitude smaller density of recombination and generation centers as compared to the majority carrier concentration. As a result, the particle-induced introduction of defects (i.e., recombination centers) will impact the minority carrier lifetime well before there is a noticeable reduction in carrier concentration (although devices with lightly doped active regions are most susceptible to degradation caused by carrier removal). Likewise, defects produced in depletion regions act to decrease the generation lifetime (and hence increase the dark current) well before noticeable reductions in the carrier concentration. Mobility degradation is not generally an issue except at very high displacement damage levels. Hence, devices whose primary characteristics depend on minority carrier or generation lifetimes will be most sensitive to displacement damage. In general, MOS devices (with the key exception of detectors) are not limited by DDD effects since they depend on majority carrier transport. Examples of device parameters impacted by DDD-induced reductions in the minority carrier lifetime include gain reduction in bipolar phototransistors used in optocoupler hybrids, reduced responsivity in photodiodes, decreased solar cell efficiency, etc. Semiconductor light sources, such as lasers and LEDs, are generally relatively radiation hard since the carrier lifetimes in the active device regions are very short. However, amphoterically doped LEDs, employed in some optocouplers, are a notable exception and are quite sensitive to particle-induced displacement damage.
III–V Detectors
Published in Antoni Rogalski, Infrared and Terahertz Detectors, 2019
Pines and Stafsudd have reported photoconductive data on high-quality n-type InSb photoconductors [105]. Their studies show that the parameters of surface-passivated detectors are limited by bulk material properties. Figure 16.18 shows the responsivity and noise as a function of temperature in an n-type photoconductive detector. At higher temperatures, the responsivity and noise depend slightly on the background photon flux density. The roll-off in responsivity and noise at higher temperatures can be correlated with the decrease in the carrier lifetime and the increase in the majority carrier concentrations.
Forty years of the Staebler–Wronski effect
Published in Philosophical Magazine, 2018
Satish Chandra Agarwal, Shobit Omar
It is clear that recombination of excess carriers in a-Si:H produce Si dangling-bond defects. These reduce the photo-carrier lifetime and reduce the efficiency of solar cells. The SWE is a consequence of the need to incorporate hydrogen into the amorphous Si network to make this material useful for electronic devices. The naturally over-constrained structure releases its strain by producing a network of voids resulting in a 5% density deficit. The about 8 at.% hydrogen is clustered in the voids and atomically dispersed in the bulk of the material, in addition to some molecular hydrogen in the voids. This complicated and inhomogeneous structure can be simulated by a model in which the band gap fluctuates spatially, having regions resembling heterojunctions and others resembling p–n junctions.
Effect of space radiation on CTJ new version multijunction solar cells
Published in Radiation Effects and Defects in Solids, 2021
B. R. Uma, Sheeja Krishnan, V. Radhakrishna, Roberta Campesato
Radiation creates displacement damage and results in defects in the solar cells. The defects induced by radiation causes a reduction in the minority carrier lifetime. This results in reduction in the voltage–current (VI) performances of the solar cells under the AM0 spectrum. The reduction depends on the type of radiation, on its energy and on the total fluence. The radiation affects the series and shunt resistance of the solar cells due to induced defects (15,16).