Semiconductor structures and CO2 laser radiation. Investigation of interaction

Jonas Gradauskas

Review of scientific publications

Reviews of scientific publications are not being sold



Physical sciences, physics (02P)

The survey involves the results of scientific research carried out by the author in the period of 1995–2010 at the former Semiconductor Physics Institute and partly at Vilnius Gediminas Technical University. 36 scientific publications are reviewed. The investigations were mainly focused on the peculiarities of interaction of a CO2 laser radiation with nonhomogeneous semiconductor structures having l-h or p-n junctions, being of asymmetrically necked forms or containing ohmic or Schottky type metal-PbTe junctions. Though the leading interest of the research had fundamental character, still the actual aspects of application of the obtained results were kept in mind as well.

The major results achieved during the research can be summarized as follows:

Wide band-gap semiconductor GaAs and GaAs/AlGaAs structures containing n-n + and p-p + junctions are suitable for the detection of CO2 laser radiation. The photoresponse is fast, of nanosecond duration, and it is determined by the hot carrier effects. Heterojunctions demonstrate higher responsivity compared to that of homojunctions. Asymmetrically necked GaAs and GaAs/AlGaAs structures show capability to detect electromagnetic radiation of wide frequency range, from microwaves up to the infrared including the terahertz band.

The magnitude of the photoresponse is dependent on the orientation of the infrared radiation polarization in respect of the axis of nonhomogeneity of asymmetrically necked or l-h structure. An idea of optoelectronic semiconductor analyzer of infrared radiation is proposed.

Electromotive force generated across GaAs p-n junction is caused by free carrier heating and is markedly lower than that across the l-h junction. The magnitude of photocurrent flowing through the p-n structure can be varied by an order with external bias voltage.

It is established that AlAs mole fraction x influences hot carrier photocurrent flowing through the GaAs/AlxGa1–xAs structures: the maximum current value increases with x in the interval 0 ≤ x ≤ 0.2, while at x = 0.3 it demonstrates a sharp drop.

The free carriers heating by means of the radiation causes decrease of the dark current in a tunnel GaAs diode.

P-n diode operating in the breakdown regime demonstrates tens of times higher sensitivity to the infrared radiation than the one operating in the forward-biased regime. The effect is based on the thermal reduction of the dark breakdown current. Microplasmic breakdown can be controlled by infrared radiation.

The photoresponse induced in narrow band-gap semiconductor HgCdTe, InSb and PbTe p-n junctions may be determined by: carrier generation, carrier heating and lattice heating. Experimental results show that several of these effects may simultaneously influence the photoresponse; it depends on the design of the structure, temperature, light intensity ratio between the photon energy and the band-gap. Note that the hot carrier electromotive force has polarity opposite to that of carrier generation caused one.

The origin of photoresponse across the closed p-n junction or metalinsulator-semiconductor structure is caused by the hot carrier induced variation of the capacitance. The proposal of an original optoelectronic device, infrared photovaractor, has been put forward.

Photoresponse induced by the CO2 laser radiation across an ohmic metal-PbTe contact is due to crystal lattice heating and thermoelectromotive force caused by temperature gradient. Meanwhile, the photoresponse induced across the Schottky metal-PbTe junction at liquid nitrogen temperature is caused by the generation of carrier pairs due to two-photon absorption, by their thermal generation and separation in the potential field of the junction; however, the thermoelectromotive force of the same polarity is present as well.

At low temperatures, CO2 laser radiation causes increase of electrical conductivity in p-Ge samples compensated with Au and Ni impurities. The reason of this effect is not mostly determined by the excitation of holes from deep impurity energy levels, but is mainly stimulated by the percolation character of hot hole electrical conductivity.

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145×205 mm
32 p.
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