Nonequilibrium devices for infra-red detection

An enhanced computer program has been applied to explain in detail the photon recycling effect which drastically limits the influence of radiative recombination on the performance of p-on-n HgCdTe heterostructure photodiodes. The computer program is based on a solution of the carrier transport equations, as well as the photon transport equations for semiconductor heterostructures. We distinguish photons in two energy ranges according to p + and n region with unequal band gaps. As a result, both the distribution of thermal carrier generation and recombination rates and spatial photon density distribution in photodiode structures have been obtained. The general conclusion, similar to our earlier work concerning 3-lm n-on-p HgCdTe heterostructure photodiodes, confirms the previous assertion by Humphreys that radiative recombination does not limit HgCdTe photodiode performance.

Section: Results Of Calculationsmentioning

confidence: 85%

Numerical Estimations of Carrier Generation–Recombination Processes and the Photon Recycling Effect in HgCdTe Heterostructure Photodiodes

Jóźwikowski

Kopytko

Rogalski

2012

“…12 denotes electron and hole diffusion noise, respectively. 8,11 In Eq. 13 F C t ð Þ denotes the fluctuation of heat stream and G C t ð Þ is the fluctuation of heat generation rate.…”

Section: Methods Of Analysismentioning

confidence: 99%

“…At present, due to the development of molecular beam epitaxy (MBE) and metalorganic vapour phase epitaxy (MOCVD) technology in the manufacturing of HgCdTe heterostructures, as well as the theories of fluctuation phenomena, we try to find ways to limit G-R noise without the LN cooling of detectors. Two examples of such solutions are small-area, noncooled 2-11 lm IR photovoltaic detectors optically immersed, 7 or a method proposed by British scientists, 8,9 which is based on the non-equilibrium mode of operation. The latter, leading to the suppression of Auger G-R processes by decreasing the freecarrier concentration below its equilibrium value was demonstrated in n-type HgCdTe photoconductors 9,10 and photodiodes.…”

Section: Introductionmentioning

confidence: 99%

Dislocations as a Noise Source in LWIR HgCdTe Photodiodes

Jóźwikowski

Jóźwikowska

Martyniuk

2016

The effect of dislocation on the 1/f noise current in long-wavelength infrared (LWIR) reverse biased HgCdTe photodiodes working at liquid nitrogen (LN) temperature was analyzed theoretically by using a phenomenological model of dislocations as an additional Shockley-Read-Hall (SRH) generation-recombination (G-R) channel in heterostructure. Numerical analysis was involved to solve the set of transport equations in order to find a steady state values of physical parameters of the heterostructure. Next, the set of transport equations for fluctuations (TEFF) was formulated and solved to obtain the spectral densities (SD) of the fluctuations of electrical potential, quasi-Fermi levels, and temperature. The SD of mobility fluctuations, shot G-R noise, and thermal noise were also taken into account in TEFF. Additional expressions for SD of 1/f fluctuations of the G-R processes were derived. Numerical values of the SD of noise current were compared with the experimental results of Johnson et al. Theoretical analysis has shown that the dislocations increase the G-R processes and this way cause the growth of G-R dark current. Despite the fact that dislocations increase both shot G-R noise and 1/f G-R noise, the main cause of 1/f current noise in LN cooled LWIR photodiodes are fluctuations of the carriers mobility determined by 1/f fluctuations of relaxation times. As the noise current is proportional to the total diode current, growth of G-R dark current caused by dislocations leads to the growth of noise current.

“…Significant improvements have been achieved by reducing the absorber volume using optical immersion, 4 doubleor multiple-pass IR radiation, 4 suppression of Auger thermal generation in nonequilibrium photoconductors, 13,14 photodiodes, [15][16][17][18] magnetoconcentration effect detectors, 19,20 and recent barrier detectors. [21][22][23][24] Nonequilibrium devices require significant bias current and exhibit excessive low-frequency noise that extends up to the MHz range.…”

Section: Introductionmentioning

confidence: 99%

Optimization of a HOT LWIR HgCdTe Photodiode for Fast Response and High Detectivity in Zero-Bias Operation Mode

Kopytko

Kębłowski

Madejczyk

et al. 2017

Fast response is an important property of infrared detectors for many applications. Currently, high-temperature long-wavelength infrared HgCdTe heterostructure photodiodes exhibit subnanosecond time constants while operating under reverse bias. However, nonequilibrium devices exhibit excessive low-frequency 1/f noise that extends up to MHz range, representing a severe obstacle to their widespread application. Present efforts are focused on zero-bias operation of photodiodes. Unfortunately, the time constant of unbiased photodiodes is still at the level of several nanoseconds. We present herein a theoretical investigation of device design for improved response time and detectivity of long-wavelength infrared HgCdTe photodiodes operating at 230 K in zero-bias mode. The calculation results show that highly doped p-type HgCdTe is the absorber material of choice for fast photodiodes due to its high electron diffusion coefficient. The detectivity of such a device can also be optimized by using absorber doping of N A = 1 9 10 17 cm À3 . Reduction of the thickness is yet another approach to improve the device response. Time constant below 1 ns is achieved for an unbiased photodiode with absorber thickness below 4 lm. A tradeoff between the contradictory requirements of achieving high detectivity and fast response time is expected in an optically immersed photodiode with very small active area.