One of the most interesting effects of nipi structures is the lifetime enhancement of excess carriers due to the built in bandedge modulation which separates the optically generated e-h- pairs in space and finally leads to an enhancement of the response. However, the lifetime enhancement generally slows down the detector speed. We present a nipi based detector concept which takes advantage of the enhanced response, but at the same time allows us to reduce the response time far below the characteristic lifetime in such structures. The physical background of the concept is presented in a theoretical model which can be understood in terms of the enhanced ambipolar diffusion and the local control of the balance of carrier generation and recombination by applying a lateral external current between two selective contacts. Results of numerical simulations are compared to experimental data obtained from selectively contacted PbTe single period (p-n-p) nipi-structures.
The concept of selectively contacted PbTe p-n-p or p-i-n-i-p structures offers interesting new features for IR-detection. As shown by a simple model and demonstrated by photo Hall and time resolved photoconductivity measurements, an enhancement of the photoconductive response beyond the expected effect of the optically generated carriers results. Control of the response time is available by background illumination. The photo Hall effect itself represents another new detection principle.
KEYWORDS: Interfaces, Information operations, Doping, High speed photonics, Resistance, Temperature metrology, Lithium, Bistability, Stereolithography, Neodymium
Single period nipis (i.e. pnp-structures) turn out to be interesting elements for the design of arbitrary
nipi-potentials. In addition, the possibility of applying selective contacts to n-type layers allows the use of p-type
buffer layers on either side of the pnp-structure in order to screen band bending effects both at the buffer
interface and at the surface. From transient photoconductivity experiments typical lifetimes result up to the
millisecond time regime (i.e. about iO to iO times the bulk lifetimes). The amplitude of the photoconductive
response cannot be attributed to simply an equivalent change of the electron density in the selectively contacted
n-layer. This fact is confirmed by Photo Hall experiments. The enhancement of the response can be explained in
terms of the special characteristics of the narrow gap material PbTe. Additional tuning of the electron densities
via background illumination is performed in order to control the lifetimes. The resulting trends are well
understood if the modification of the nipi-potential caused by excess carriers is taken into account. In a simple
model the role of the background radiation is explained.
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