Doping of the lead telluride and related alloys with the group III impurities results in appearance of the unique physical features of a material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), high radiation hardness and many others. We present the physical principles of operation of the photodetecting devices based on the group III-doped IV-VI including the possibilities of a fast quenching of the persistent photoresponse, construction of the focal-plane array, and others. We report on the performance of lead telluride-based single direct detectors. The optical NEP on the order of 10-19 W/Hz1/2 at T=1.57 K has been demonstrated at the wavelength of 350 m. The advantages of terahertz photodetecting systems based on the group III-doped IV-VI are summarized.
Doping of the lead telluride and related alloys with the group III impurities results in appearance of the unique physical
features of a material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100
photoelectrons/incident photon), radiation hardness and many others. We present the physical principles of operation of
the photodetecting devices based on the group III-doped IV-VI including the possibilities of a fast quenching of the
persistent photoresponse, construction of the focal-plane array, new readout technique, and others. The advantages of
infrared photodetecting systems based on the group III-doped IV-VI in comparison with the modern photodetectors are
summarized. The spectra of the persistent photoresponse have not been measured so far because of the difficulties with
screening the background radiation. We report on the observation of strong persistent photoconductivity in
Pb0.75Sn0.25Te(In) under the action of monochromatic submillimeter radiation at wavelengths of 176 and 241 microns.
The sample temperature was 4.2 K, the background radiation was completely screened out. The sample was initially in
the semiinsulating state providing dark resistance of more than 100 GOhm. The responsivity of the photodetector is by
several orders of magnitude higher than in the state of the art Ge(Ga). The red cut-off wavelength exceeds the upper limit
of 220 microns observed so far for the quantum photodetectors in the uniaxially stressed Ge(Ga). It is possible that the
photoconductivity spectrum of Pb1-xSnxTe(In)covers all the submillimeter wavelength range.
Doping of the lead telluride and related alloys with the group III impurities results in appearance of the unique physical
features of a material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100
photoelectrons/incident photon), radiation hardness and many others. We present the physical principles of operation of
the photodetecting devices based on the group III-doped IV-VI including the possibilities of a fast quenching of the
persistent photoresponse, construction of the focal-plane array, new readout technique, and others. The advantages of
infrared photodetecting systems based on the group III-doped IV-VI in comparison with the modern photodetectors are
summarized. The spectra of the persistent photoresponse have not been measured so far because of the difficulties with
screening the background radiation. We report on the observation of strong persistent photoconductivity in
Pb0.75Sn0.25Te(In) under the action of monochromatic submillimeter radiation at wavelengths of 176 and 241 microns.
The sample temperature was 4.2 K, the background radiation was completely screened out. The sample was initially in
the semiinsulating state providing dark resistance of more than 100 GOhm. The responsivity of the photodetector is by
several orders of magnitude higher than in the state of the art Ge(Ga). The red cut-off wavelength exceeds the upper limit
of 220 microns observed so far for the quantum photodetectors in the uniaxially stressed Ge(Ga). It is possible that the
photoconductivity spectrum of Pb1-xSnxTe(In)covers all the submillimeter wavelength range.
The work deals with studies of the grain size and surface state effect on photoelectric and transport properties of
PbTe(In) films in the temperature range from 4.2 K up to 200 K under irradiation of a blackbody source and terahertz
laser pulses. The PbTe(In) films were deposited on insulating substrates kept at the temperatures TS equal to -120 (see manuscript)
250C. AFM, SEM, Auger spectroscopy and X-ray diffraction were used to study the film microstructure. Increase of the
TS value led to mean grain size growth from 60 up to 300 nm. All films had a column-like structure with the columns
nearly perpendicular to the substrate plane. It is shown that microstructure of the films strongly affects the
photoconductivity character in the terahertz region of the spectrum. Positive persistent photoresponse is observed at low
temperatures in the polycrystalline films. For these films transport and photoelectric properties are determined by the
grain volume and impurity state specifics. Nanocrystalline films have all features of non-homogeneous systems with
band modulation. For these films only negative photoconductivity is observed in the whole temperature range. Possible
mechanisms of the photoresponse formation are discussed.
We have analyzed photoconductivity in PbSnTe(In) under the action of ~100 ns long terahertz laser pulses with the
wavelength 90 - 500 μm in the temperature range 4.2-300 K. Strong photoresponse has been observed at all wavelengths
used. Positive persistent photoconductivity is observed at T < 10 K, whereas negative non-persistent photoresponse
prevails at higher temperatures T ~ 25 K. Specific features of photoconductivity are discussed.
Photoelectric, transport and optical properties are studied for nanostructured PbTe(In) films. Synthesis of the films was
performed using evaporation of a target source to a glass substrate. The films have column-like structure with a mean
grain size varying from about 60 nm to 170 nm depending on the substrate temperature. Analysis of the data obtained
revealed that the conductivity of the films is determined by two mechanisms: charge transport along the inversion
channels at the grain surface and activation through barriers at the grain boundary. Persistent photoconductivity appears
in the films below T = 150 K. The frequency dependence of the relative photoresponse has a pronounced maximum. The
photoresponse in the ac mode may be by two orders of magnitude higher than in the dc measurements.
Doping of the lead telluride and related alloys with the group III impurities results in appearance of unique physical features of a material, such as persistent photoresponse, enhanced responsive quantum efficiency (up to 100 photoelectrons/incident photon), radiation hardness and many others. As a result, single photodetectors based on Pb1-xSnxTe(In) demonstrate extremely high performance in the Terahertz wavelength range. Furthermore, it is shown that local long-lived non-equilibrium states are generated in Pb1-xSnxTe(In) alloys at low temperatures under the action of local Terahertz excitation. This result opens a possibility for construction of a "continuous" focal-plane array for detection of Terahertz radiation. Ideas for readout of information from this array are discussed.
We present results of the studies of photoconductivity and transient processes in n-PbTe(Ga) epitaxial films of thickness approximately 0.2 micrometer prepared by the hot wall technique on BaF (formula available in paper) substrates. The photoelectric properties are investigated in the temperature range 4.2 - 300 K under infrared (IR) illumination by GaAs light-emitting diode with (lambda) equals 1 micrometer and by a white light lamp. The low-temperature measurements reveal the IR-photoconductivity threshold at TC approximately equals 150 K (for the flux density (formula available in paper), that exceeds by 40 K and 70 K the temperatures relevant to more thick films (approximately 2 micrometer) and to single crystals, respectively. This substantial increase of TC in thin films gives us an opportunity to estimate the recombination barrier of Ga impurity in PbTe.
The photoelectric and kinetic properties of n-PbTe(Ga) films prepare don the BaF2 and Si substrates by hot wall epitaxy technique have been investigated in the temperature T interval 4.2 divided by 300 K. The photoelectric measurements show that all photosensitive samples may be divided into two groups characterized by positive and negative photosensitivity to IR-illumination at temperatures close to 4.2 K. The kinetics of positively photosensitive films is found to be similar to the kinetics of the bulk n-PbTe(Ga) single crystals of high resistance. The photoresponse of negatively photosensitive films appears to be composed from two parts. They are the dominant negative photosensitivity and a positive photoconductivity signal characterized by significantly faster kinetics. The experimental result are discussed in terms of DX-like behavior of the impurity centers.
The thermally induced currents (TIC) and instabilities of photoresponse in Pb1-x-ySnxGeyTe(IN) films on BaF2 substrates have been investigated at temperatures 4.2 < T < 30 K. The temperature TM corresponding to maximum values of single TIC peaks appears to be extremely low varying from 6 K up to 14 K. The combined effect of lighting and slight heating of the sample from 4.2 K up to approximately 6 K results in photoresponse instabilities depending on the experimental regime. The results are interpreted in terms of thermal excitation of charge carriers from metastable impurity level.
The analysis of photoconductivity (PC) spectra in PbTe(Ga) single crystals and films shows that a pronounced photoresponse is observed at an energy approximately 20 meV less the energy gap value. The relative amplitude of the sub-band photoresponse depends on the method of the crystal synthesis, but its energy position does not depend on temperature or growth technique. For PbTe(Ga) thin films the structure of the absorption edge is similar to undoped PbTe and amplitude of the sub-band photoresponse appears to be small. The phenomenological description of the PC kinetics of the investigated samples under the IR-radiation of pulse and heat sources is done. It is established that under the radiation with pulse duration 10 mcs the characteristic relaxation times are 10-3 s at 4.2 K, and the persistent PC can be observed only under the continuous radiation at T < 80 K. Moreover, at low intensities of the continuous radiation PC relaxation time is about 1 ms and only the increase of radiation intensity results in appearance of the persistent PC with the relaxation times of 105 s. We propose a phenomenological model of energy spectrum and impurity states in PbTe(Ga), which is able to describe the experimental data. According to this model the metastable impurity states 20 meV lower the bottom of the conduction band exist in addition to the ground states 70 meV lower the bottom of the conduction band. The increase of the radiation intensity provides the growth of the metastable states concentration and the impurity band formation. So it can be concluded that PbTe(Ga) may be considered as an advanced material for the multispectral photodetectors operating in near IR-region if the ground state electrons are excited and in far IR-region if the excited from preliminary induced metastable states.
The effect of deep electron irradiation on the galvanomagnetic and photoelectric properties of p- and n- type PbTe single crystals doped with gallium have been investigated. It has been found that electron irradiation of p-type samples results in the decrease of the holes concentration, the p-n-conversion and the transition of irradiated crystals to a dielectric state. In all investigated samples long-term relaxation processes and effect of persistent photoconductivity at low temperatures have been revealed. Under the electron irradiation the photoresponse in the p-type samples with low gallium concentration monotonously increase up to the point of transition to the dielectric state. In the dielectric state gallvanomagnetic and photoelectric parameters of the samples do not depend on the irradiation fluence whether it has been achieved by means of sufficient doping or slight initial doping followed by the electron irradiation and PbTe doped with gallium possesses high radiation hardness of galvanomagnetic parameters.
The most important features of Pb1-xMnxTe(In) solid solutions are the effect of Fermi level (FL) pinning and the existence of metastable electronic states resulting in the appearance of the relaxation processes of long duration. The increase of MnTe content in Pb1-xMnxTe(In) leads to the shift of pinned FL towards the conduction band edge Ec and metal-dielectric transition at X approximately 0.05. The kinetic processes under the radiation of Pb1-xMnxTe(In) single crystals have been investigated in the temperature range 4.2-35 K. It has been found that under the composition X variation the view of kinetic curves changes qualitatively. At X 1 of the impurity center together with the ground one E2 is assumed. It is shown, that if the shift of E1 and E2 levels relatively to Ec is characterized by the linear dependence on X, the fast relaxation appears near the point when E1 level crosses Ec and enters the energy gap.
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