Auger suppression

Nonequilibrium detectors share a number of similar or even identical characteristics, independently on a particular structure or process. This is a consequence of similar basic principles utilized for nonequilibrium operation. All of the Auger-suppressed devices utilize relatively strong external or internal fields to decrease minority carrier concentration in a given volume and thus operate in the mode of large deviations from equilibrium. The degree of suppression is proportional to the intensity of the applied fields. The structures with the decreased concentration of minority carriers are conventional intrinsic photonic detector strucmres. 

In all nonequilibrium devices presented until now the active region is fabricated in weakly doped v or t material. If a nonequilibrium mechanism is applied the majority concentration in this region decreases near to extrinsic concentration. To maintain electroneutrality, the minority carrier concentration drops several orders of magnitude more. Thus, a nonequilibrium and stationary carrier distribution is reached and dynamically maintained by means of external fields. In such a mode semiconductor behaves again as an extrinsic one. This means that Auger-suppressed devices operate in nonequilibrium mode. 

General Model of Nonequilibrium Photodetectors with Auger Suppression... 

Type of nonequilibrium Contact type Suitability for Auger suppression External electric field In n-type semiconductor External electric field In p-type semiconductor... 

Some advantages of purely electrical methods for causing nonequilibrium in Auger-suppressed detectors are given below. 

The boundary conditions for the galvanic-type Auger-suppressed devices are posed for the contacts in the points y = 0 and y = 1. While deriving them we assume that the carrier distribution on contacts is always nondegenerate [343]. Let us denote with yugr the built-in diffusion potential, while U is bias voltage and / is the potential. If we apply the condition of equality of Fermi quasi-levels on contacts we obtain... 

The further text presents an approximate consideration of transport phenomena within an exclusion device. Besides enabling us to simply determine the main parameters of exclusion stmctures, it also gives us a better insight in operation of Auger suppressed devices. It follows the approach of White [50], albeit with certain modifications that will later enable us to obtain some additional parameters. 

It can be seen in Figs. 3.9 and 3.10 that no full exclusion occurs under the applied conditions, but only partial instead. Even for the largest values of bias the carrier concentrations are not constant, majority carrier concentrations are not brought near the impurity level and minority concentrations are not below it. Further simulations show that at room temperature exclusion does improve photoconductor characteristics, but cannot lead to qualitative changes and a level of Auger suppression sufficient to furnish a BLIP device. 

A comparison between the calculated values of specific detectivity of an exclusion detector and the BLIP values for a field of view of 180° at the same cutoff wavelength (equal to performance of a photoconductive device at 77 K) shows that all of the calculated values are significandy below the BLIP limit. The detectivity increase in comparison to a photoconductor without nonequilibrium Auger suppression (conventional sub-BLIP photoconductor) is less three times. 

Technologically and physically exclusion devices are surely the simplest Auger-suppressed devices. Their operation for the most part corresponds to a conventional photoconductor in the sweepout mode. The only required additional measure to... 

The performance of the diode structures utilizing the effects of minority carrier extraction is much better than that of the exclusion photoconductors. Their leakage currents are much lower, and Auger suppression much larger at significantly lower electric fields. 

The first extraction structure for Auger suppression was fabricated in InSb [336]. It was a three-layer homojunction structure with two contacts. An extraction diode in mercury cadmium teUuride was fabricated as a three-terminal device utilizing the pseudoexclusion effect [361]. 

Fig. 3.27 Five-layered photodiode with Auger suppression incorporating two wide bandgap barrier layers...

Nowadays an important position belongs to the infrared detectors incorporating the mentioned wide-bandgap semiconductor barrier [368-370] (the BIRD detector —Barrier Infrared Detector). Maimon and Wicks proposed to use unipolar BIRDs —i.e., the built-in barrier layer blocks one carrier type, but allows free flow of the other type [371]. Such structures are for instance nBn. Ting et al. proposed the use of complementary barriers, one for electrons, another for holes, positioned at different depths [372]. Itsuno et al. analyzed NBvN and nBn detectors (where B stands for Barrier) [373, 374]. In their 2013 paper Martinyuk et al. quoted that besides Auger suppression the BIRD devices also suppress Shockley-Read-Hall g-r processes [375]. 

In a photodiode with Auger suppression the saturation current density decreases with reverse bias, thus leading to the appearance of negative differential resistance. For the above described case we calculate this current according to... 

The first experimental works dedicated to the fabrication and characterization of Auger-suppressed extraction photodetectors handled mostly homojunction devices. Ashley et al. [363] fabricated three-layer p im structures in Inj-xAlxSb. They utilized molecular beam (MBE) and (lOO)-oriented InSb substrate. The doping level of the % zone was about 10 cm , its thickness 0.75-3 pm. The dopant concentrations in highly doped zones were higher than 10 cm . Etching was used to fabricate mesa stmctures with an area of about 10 " cm and passivation with anodic oxide was used. 

Compared to other types of Auger suppressed photodetectors, extraction devices have the lowest dark currents. This means a number of their advantages over other types. Their operation is far from the hot carrier region, the level of g-r processes is lower, the problems with the stmcture heating are less pronounced. These devices are able to operate at relatively largest temperatures. 

The limit of concentration decrease of the majority carriers in the exclusion case is dopant concentration. In order to preserve electroneutrality, the concentration of minority carrier decreases several orders of magnitude more. The result is an intensive carrier depletion near the top surface and thus Auger suppression. 

Similar to all other nonequilibrium devices, Auger suppression is significant only in starting concentrations of electrons and holes are comparable (near-intrinsic material), and negligible in strongly doped semiconductor. 

A detector with a suboptimal critical thickness will have insufficient Auger suppression and decreased absorption, i.e., excessive noise levels and suboptimal quantum efficiency. The one with excessive critical thickness will in best case have performance practically identical to the optimal case, and in worst case the excessive bias will cause undesired oscillations and other hot carrier effects without contributing the detector performance. 

The possibility to tailor the composition of Hgi xCdxTe enables a continuous variation of operating temperatures, applied fields and detector dimensions to reach their optimum values for maximum specific detectivity-bandwidth product. A larger carrier depletion within the active area will not only improve signal-to-noise ratio but simultaneously shorten the response time. However, high fields easily cause transition of carriers to hot region. There is an optimum ratio between the field intensities and the beneficial influence of Auger suppression. This ratio is determined by the characteristic curve drawn between the areas A and B in Fig. 3.46. 

Tables 1.6 and 1.7 show that there are families of photonic detectors whose performance could be enhanced through nonequilibrium methods. By a convenient design which would simultaneously utilize magnetoconcentration and some of the other methods, one could expect larger Auger suppression than by applying these methods separately. Electric, magnetic, thermal field inhomogeneities could be used to that purpose.

Z. Jaksic, Z. Djuric, Cavity enhancement of Auger-suppressed detectra A way to background-limited room-temperature operation in 3—14 pm range. TEER J. Sel. Top. Quant. Electr. 10(4), 771-776 (2004)... 

P. Emelie, J. Phillips, S. Velicu, P. Wijewamasuriya, Parameter extraction of HgCdTe infrared photodiodes exhibiting Auger suppression. J. Phys. D 42(23), 234003 (2009)... 

P.Y. Emelie, S. Velicu, C.H. Grein, J.D. Phillips, P.S. Wijewamasuriya, N.K. Dhar, Modeling of LWIR HgCdTe auger-suppressed infrared photodiodes under nonequilibrium operation. J. Electron. Mat. 37(9), 1362-1368 (2008)... 

A.M. White, Auger suppression and negative resistance in low gap PIN diode strucmres. Infrared Phys. 26(5), 317-324 (1986)... 

A.M. White, Negative resistance with Auger suppression in near-intrinsic, low-bandgap photo-diode structures. Infrared Phys. 27(6), 361-369 (1987)... 

C. Jones, N. Metcalfe, A. Best, R. Catchpole, C. Maxey, N. Gordon, R. Hall, T. Colin, T. Skauli, Effect of device processing on 1/f noise in uncooled. Auger-suppressed CdHgTe diodes. J. Electron. Mat 27(6), 733-739 (1998)... 

Z. JakSid, Z. Djuric, Optimized high-frequency performance of Auger-suppressed magnetoconcentration photoconductors. Microelectron. J. 31(11-12), 981-990 (2000)... 

Z. JakSic, Z. Djuric, Extraction Photodiodes with Auger Suppression for All-Weather Free-Space Optical CommunicatioiL Electronics 8(1), 30-32 (2004)... 

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