Magnetoconcentration

It is only to be expected that some nonequilibrium detector stmctures have their analogs in semiconductor lasers. Exclusion detectors correspond to single-hetero-lasers, extraction devices to double-heterolasers, and magnetoconcentration detectors to lasers with the magnetoelectric photoeffect proposed by Marimoto et al. [331]. This inverse analogy is valid not only in electrical, but also in optical field, where e.g., resonant cavity (RCE) detector structures are connected with VCSEL lasers, and lasers with a PBG cavity with PCE (photonic crystal-enhanced) detectors. 

Extraction diodes are the most advanced of all nonequilibrium detectors. The fabrication of these detectors is fully compatible with standard narrow-bandgap semiconductor technologies and with standard detector circuitry. Their function does not cause interference with surrounding circuitry, as is the case with magnetoconcentration devices. 

Magnetoconcentration or Suhl effect (Harry Suhl) [393] utilizes crossed electric and magnetic fields directed in parallel to the surface of a single crystalline semiconductor slab (here the photodetector), as shown in Fig. 3.44. The presented... 

Magnetoconcentration detectors could straightforwardly benefit from the use of microfabrication technologies, since this would mean smaller permanent magnets and thus more compact devices, but also fields at the same time higher and better confined. 

If the Lorentz force is oriented from the active area, charge carriers are pushed into the bulk. If their free path is larger than the slab thickness, most of the carrier reaches the bottom surface and accumulates there. Thus magnetoconcentration is a change of spatial distribution of carriers caused by crossed electric and magnetic field. 

The level of suppression will depend on thermal generation rate and the intensity of applied field. It is usually said that magnetoconcentration plays a significant role at high fields and large injections [394]. 

A biased photoconductor under the influence of magnetoconcentration for the case of low magnetic fields was investigated by Malyutenko and Teslenko [397, 398]. They denoted the effects of Lorentz force to carriers in such a device the transversal sweep-out ( a semiconductor with induced anisotropy of conductivity ). Their work included both theoretical and experimental investigation, and the magnetic induction they utilized did not exceed 0.2 T. 

A magnetoconcentration detector is described by the set of equations (3.57) to (3.64). The continuity equations have the identical form to (3.65) and (3.66). Current density in the direction of the magnetic field is given by (3.59). Together with the electroneutrality equation (3.63) and (3.64) one obtains a second order differential equation for the minority carrier concentration. For n-type semiconductor this equation is... 

The boundary conditions for the carrier transport equation in the magnetoconcentration detector are posed for the top and bottom surface, assuming that their surface recombination rates are described by the Shocldey-Read model, i.e., that S = 1/tno = 1/tpo- The second assumption often met in literature (e.g., [401]) is that the trap distribution function at the surface is always of Maxwell-Boltzmaim type (nondegenerate semiconductor). In that case Shockley-Read expression for recombination rate (1.70) becomes... 

Galvanomagnetic Methods—Magnetoconcentration Photodetector where the coeflftcients a and b are... 

Fig. 3.45 Results of approximate analytical model of magnetoconcentration detector and their comparison with numerical simulation according to full mode, a Critical thickness versus bias for a magnetoconcentration HgCdTe p-type photodetector for different values of magnetic induction r = 220 K, X = 0.187, d = 15 pm,...

No = 10 m . Dashed line numerical calculation using accurate model full lines analytical approximation, b Spatial dependence of carrier concentration across the magnetoconcentration EMCD device (y-axis)... 

Figure 3.46 shows the distribution of minority carriers in p-type nonequilibrium magnetoconcentration photodetector for different values of bias voltage. Larger values of bias and thicker detector slabs mean stronger depletion (several orders of magnitude). 

Fig. 3.50 Shockley-Read process rates across a magnetoconcentration Hgi xCdxTe photodetector for different values of bias voltage. Solid recombination, dotted generation. Numbers near each curve denote bias voltage in volts, x = 0.186, T = 220 K, S = 2 T, = 5 x 10 m. ...

Current-Voltage Characteristics of Nonequilibrium Magnetoconcentration Photodetectors... 

Figure 3.51 shows the dark current profile across the magnetoconcentration photodetector for different operating temperatures. As expected, the rise of the operating temperature increases dark current. Figure 3.52 shows the same dependence for different values of bias voltage at 220 K. 

Fig. 3.51 Spatial distribution of dark current of a magnetoconcentration detector for different operating temperatures...

Fig. 3.53 Spatial distribution profile for signal current across HgCdTe magnetoconcentration detector...

The total current of a magnetoconcentration photodetector in x direction is obtained as the integral of the expression for J(y) over all values of y ... 

Assume that the external electric field may be approximately expressed as a ratio between the bias voltage and the sample length, E = Ull. This is valid if the electric field dependence on the position x is linear, which is satisfied for sufficiently depleted photodetector. In that case the current-voltage characteristics of the magnetoconcentration photodetector is given as... 

Fig. 3.54 Calculated U1 characteristics of magnetoconcentration photodetector at different temperatures...

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