Semiconductor diode with suppression of auger generation process

Details Semiconductor diode with suppression of auger generation process Semiconductor diode with suppression of auger generation process

1998-03-30

2000-06-27

Crane, Sara

Active solid-state devices (e.g., transistors, solid-state diode

Responsive to non-electrical signal

Electromagnetic or particle radiation

257442, 257614, 257656, H01L 3100

Patent

active

06081019&

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a semiconductor diode structure which gives rise to improved performance at room temperatures.
Narrow gap semiconductors have hitherto found few applications around room temperatures because the intrinsic carrier concentrations are so high that they mask doping concentrations and lead to very high thermal generation rates with high leakage currents, high noise and low radiative efficiency in emitters. Therefore they are typically cooled.
In order to capitalise on the potentially very high speed and very low power dissipation of narrow gap devices, Auger Suppressed devices were invented (see for example Proc. SPIE, Infra-red Technology XI Vol 572 (Aug 20, San Diego Calif.) 1085, pp. 123-132). By electronic means the carrier concentrations in an active zone are reduced even at ambient temperatures or above so that extrinsic behaviour is achieved.
This is done by sandwiching a low doped layer between two contacting zones with interfaces of special properties. The first zone forms an excluding interface and might have high doping of the same type as the active zone, high band gap, low doping same type or a combination of both features. The important feature of the first zone is that the minority concentration is very low so that in reverse bias (that which drives minority carriers in an active zone away from the interface) carriers are removed from the active zone without replenishment from the first zone. The interface between such a zone and the layer into which minority carriers cannot pass (in this case the active layer) is known in an excluding interface.
In cadmium mercury telluride (CMT), for example, at room temperature this phenomenon exists over a wide range of material parameters. It is sufficient only that the minority carrier concentration in the contacting zone is lower than in the active zone. Typical doping in the active layer might be below 5.times.10.sup.15 p-type with the contact zone more than 10.sup.17 p-type, with or without a band gap increase in the contact zone of several times kT.
The excluding layer may be several microns thick, sufficient to minimise the in-diffusion of minority carriers from the biasing contact itself.
The active layer may be several microns thick. It is usual to make it not much more than the diffusion length of the minority carrier in the active zone, and preferably much less. For a p-type active layer, five microns might be a typical value. For n-type doping, typical values would be much less (less than two microns). This aspect is addressed in patent publication EP0401 352B1.
Suppression will occur to some degree, whatever the length of the active layer. The active layer is terminated by a second contact zone, with doping of opposite type as in a junction. Again, the lower minority carrier concentration in this final layer, the better, and similar specifications apply to this as do to the first contact zone (except that the doping is of the opposite type).
With the bias in the same direction as before, minority carriers are captured at the interface and cannot return (in this case because of the usual barrier which exists in a reverse biased junction). Minority carriers migrate to the junction partly under the influence of the bias electric field, and partly by diffusion. Such an interface between two zones, which allows carriers to pass between zones in one direction but not the other but the other is called an extraction interface. Not all three layer devices have exclusion and extraction interfaces. If the doping and band gap conditions are not appropriate, then the application of a reverse bias will result in depletion. The conditions required for depletion for a PIN device are described in EP-A-0193 462.
The overall effect is that minority carriers are removed at the extracting contact and are not resupplied at the excluding contact. The original concentration of minority carriers is large: near the intrinsic concentration. After the application of bias it can be very low, typically below 10.sup.13, and often much lower depending

REFERENCES:
patent: 5016073 (1991-05-01), Elliott et al.
patent: 5382814 (1995-01-01), Ashley et al.
Ashley, T., et al., "Non-equilibrium devices for infrared detection," SPIE vol. 572, Infrared Technology XI, pp. 123-132, Aug. 1985.
Orsal, Bernard, et al., "HgCdTe 1.6 to 2.5 um Avalanche Photodiode . . . ," IEEE Transactions on Electron Devices, vol. 38, No. 8, pp. 1748-1756, Aug. 1991.
Belotelov, S.V., et al., "Luminescence emitted by implanted CdHgTe layers . . . , " Soviet Physics, Semiconductors, 25(6), pp. 637-641, Jun. 1991.
Elliott, C.T., et al., "MOVPE grown heterojunction diodes in HgCdTe," SPIE vol. 2269 Infrared Technology XX, pp. 648-657, Jul. 1994.

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