Photoelectromagnetic Research Articles

Photoelectromagnetic Effect Induced by Terahertz Laser Radiation in Topological Crystalline Insulators Pb1-xSnxTe.

Topological crystalline insulators form a class of semiconductors for which surface electron states with the Dirac dispersion relation are formed on surfaces with a certain crystallographic orientation. Pb1−xSnxTe alloys belong to the topological crystalline phase when the SnTe content x exceeds 0.35, while they are in the trivial phase at x < 0.35. For the surface crystallographic orientation (111), the appearance of topologically nontrivial surface states is expected. We studied the photoelectromagnetic (PEM) effect induced by laser terahertz radiation in Pb1−xSnxTe films in the composition range x = (0.11–0.44), with the (111) surface crystallographic orientation. It was found that in the trivial phase, the amplitude of the PEM effect is determined by the power of the incident radiation, while in the topological phase, the amplitude is proportional to the flux of laser radiation quanta. A possible mechanism responsible for the effect observed presumes damping of the thermalization rate of photoexcited electrons in the topological phase and, consequently, prevailing of electron diffusion, compared with energy relaxation.

Determination of Diffusion Length of Carriers in Graphene Using Contactless Photoelectromagnetic Method of Investigations

ABSTRACTThe photoelectromagnetic (PEM) investigations are proposed for determination of diffusion length of carriers in graphene. The presented measurements are performed in Corbino configuration using noncontact technique. The circular PEM currents are detected in an outer coil by induction if illumination intensity is periodically varied. The theoretical dependence of PEM response on magnetic field induction, intensity and spatial distribution of illumination as well as on frequency of illumination chopping is presented. Experimental PEM data are presented for graphene films grown by CVD processing on a cooper foil and transferred onto a glass substrate. The presented method of investigations should be essential for development of graphene electronic and optoelectronic devices.

Photoelectromagnetic Investigations of Graphene

The photoelectromagnetic (PEM) investigations of graphene has been done using noncontact technique. In a graphene illuminated by a circular spot, free electrons and holes are photogenerated in a region from which they diffuse in all directions in the sheet. When a magnetic field is applied perpendicularly to the graphene surface, diffusing carriers are deflected owing to the Lorentz force and so-called PEM current flows. Under amplitudemodulated illumination of a sample the PEM circulating current varies, and consequently the changing magnetic flux, caused by it, can induce a measurable voltage in suitably placed pick-up coils. The investigated samples of graphene were supplied by Graphene Supermarket. Monolayer graphene films were grown by CVD processing on a cooper foil and transferred onto a Corning EAGLE XGTM AMLCD glass substrate. The dependence of PEM response on magnetic field induction, illumination intensity for different photon energies, and frequency of illumination chopping is presented. Fitting of the experimental results with theoretical dependences have allowed determination of carrier lifetimes. Mapping of the PEM response over the investigated sample is shown, too. We anticipate our paper to be a starting point for PEM investigations of minority carrier lifetime and carrier diffusion length in graphene. Such investigations should be essential for development of graphene electronic and optoelectronic devices.

History of HgTe-based photodetectors in Poland

AbstractIn Poland, the HgCdTe studies began in 1960 at the Institute of Physics, Warsaw University. The material processing laboratory was created by Giriat and later by Dziuba, Gałązka, and others. Bridgman technique with sealed thick wall quartz ampoules was used to grow material suitable for research and experimental devices. Among the first papers published in 1961 and 1963 there were the Polish works devoted to preparation, doping, and electrical properties of HgCdTe.Infrared detector’s research and development efforts in Poland were concentrated mostly on uncooled market niche. At the beginning, a modified isothermal vapour phase epitaxy has been used for research and commercial fabrication of photoconductive, photoelectromagnetic and other HgCdTe devices. Bulk growth and liquid phase epitaxy were also used. Recently, the fabrication of infrared devices relies on low temperature epitaxial technique, namely metalorganic vapour phase deposition.At present stage of development, the photoconductive and photoelectromagnetic (PEM) detectors are gradually replaced with photovoltaic devices which offer inherent advantages of no electric or magnetic bias, no heat load and no flicker noise. Potentially, photodiodes offer high performance and very fast response. However, conventional photovoltaic uncooled detectors suffer from low quantum efficiency and very low junction resistance. The problems have been solved with advanced band gap engineered architecture, multiple cell heterojunction devices connected in series, and monolithic integration of the detectors with microoptics.In final part of the paper, the Polish achievements in technology and performance of HgMnTe and HgZnTe photodetectors are presented.

Application of high-frequency contactless method of PEM investigations to examine near-surface layer of Si and GaAs

The recently reported contactless photoelectromagnetic (PEM) method of determining carrier lifetimes was used to investigate Ga : AS : Te and Si : B samples with polished and grinded surfaces. In the presented experiments the samples were illuminated with radiation of different wavelengths (and different absorption coefficients) emitted by diode lasers, argon and HeNe lasers acoustooptically modulated up to 100 kHz. The frequency dependence of PEM magnetic flux registered for cases of excess carriers photogeneration at different depths in a sample are presented and fitted with theoretical dependencies. It allows an evaluation of the bulk and near-surface region electron and hole lifetimes.

The photoelectromagnetic effect in planar silicon structures

The photoelectromagnetic (PEM) effect is a multiplyingeffect, which means that the electrical output signal is proportional to a product of two physical parameters. For the PEM effect the voltage is proportional to the product of a magnetic flux density and an irradiance. This paper examines PEM structures fabricated using silicon planar technology and shows that their performance as a multiplier is comparable to that of other semiconductors.

Recombination parameters of epitaxial CdxHg1-xTe/CdTe layers from photoelectromagnetic and photoconductive effects

It is shown that photoconductivity (PC) of thin epitaxial CdxHg1-xTe/CdTe layers in the stationary crossed fields has a complicated non-monotonic behaviour as a function of magnetic field. The analytical expressions for PC and the photoelectromagnetic (PEM) effect, including diffusion, gradient and photoconductive components, are presented and qualitative physics is discussed. The experiments were carried out on liquid-phase epitaxial CdxHg1-xTe/CdTe films of p-type conductivity with x approximately=0.2 at liquid-nitrogen temperature. On the basis of the combined analysis of PC and PEM effects a set of the recombination and diffusion parameters was determined: the volume lifetime, the diffusion length, the surface recombination velocities and the internal electric field due to the composition gradient. Also, it is shown that from the PC measurements in different electric fields one can obtain information about variation of the parameters across the layer.

Mercury Zinc Telluride 10.6 µm Ambient Temperature Photodetectors

Theoretical and experimental investigations of mercury zinc telluride (MZT) ambient temperature longwavelength photodetectors are reported. The ultimate detectivities of MZT photoconductors (PC), photodiodes, photoelectromagnetic (PEM) and Dember detectors at 10.6 pm have been calculated as a function of material composition, doping and geometry of the devices. The high-temperature longwavelength PC and PEM detectors have been fabricated from Cu-doped bulk MZT crystals grown by a modified quench/anneal technique. The measured performance has been confronted with theoretical predictions showing good overall agreement. It is concluded that the high figure of merit, stability and hardness of MZT make this material superior in comparison to mercury cadmium telluride and that it will replace the latter in application for high-temperature photodetectors. The performance of high-temperature MZT photodetectors can be further improved by the use of optical resonant cavity and optical immersion. These devices exhibit detectivity by several orders of magnitude higher than thermal detectors with subnanosecond response time, and can achieve performance comparable to that of slow thermal detectors.

Interference photoconductivity and photoelectromagnetic effect in amorphous silicon.

The existence of the so-called interference photoconductivity (PC) and photoelectromagnetic (PEM) effects in the investigated thin films of a-Si:H,F is shown. These effects appear due to interference of radiation in a sample. In this paper, the fitting of interference PC and PEM responses to theoretical relationships is presented. Values of carrier lifetime, diffusion length, and surface recombination velocity have been estimated. Spectral dependences of individual quantum efficiency coefficients for PC and PEM effects can give information about energy distribution and type of electronic states in the investigated samples. Influence of radiation intensity on optical and recombination parameters of the material is shown.

Hole mobility in HgI 2

Hole mobility along the layers in HgI 2 has been measured for the first time by the nuclear techniques using alpha particles and by cutting the sample perpendicularly to the layers. The value of the hole drift mobility is in agreement with previous results obtained by Photo-Electro-Magnetic (PEM) effect and it is much higher than hole drift mobility along the c-axis.

On the Performance of Non-Cooled (In, As)Sb Photoelectromagnetic Detectors for 10.6 m Radiation

Using a generalized theory of the photoelectromagnetic (PEM) effect, the parameters of non-cooled InAs0.35Sb0.65 PEM far-infrared detectors are analysed. The responsivity Rv and detectivity D* are estimated in dependence of detector geometry and of recombination velocities at the surface. The highest values for Rv ≈ 0.1 V/W and for D* ≈ 105 m Hz1/2 W−1 at λ = 10.6 μm are obtained for p-type material with p/ni ≈ 10. [Russian Text Ignored].

Interference photoelectromagnetic effect in graded-gap semiconductors

Numerical calculations describing the influence of the interference of internally-reflected radiation on the photoelectromagnetic (PEM) effect in graded energy-gap Cd x Hg 1− x Te structures are presented. The spectral voltage responsivities of graded-gap IR-PEM detectors are reported as functions of the semiconductor structure thickness, composition profile of the structure, doping level, surface recombination velocity and reflection coefficient from the structure substrate. The thickness of graded-gap PEM detectors is one of the more important parameters which can affect their performance.

The Influence of Surface Recombination on the Photoelectromagnetic (PEM) Effect in Semiconductors with Deep Traps

The Influence of Surface Recombination on the Photoelectromagnetic (PEM) Effect in Semiconductors with Deep Traps

On the performance of non-cooled CdHgTe photoelectromagnetic detectors for 10.6 μm radiation

Using a generalized theory of the photoelectromagnetic (PEM) effect, the parameters of CdHgTe PEM far-infrared detectors are analysed. The normalized responsivity, R v, detectivity D ∗ and time constant τ are determined, dependent on detector geometry and recombination velocities at the surface and in the volume of the sample. In CdHgTe at 300 K and for wavelengths λ > 8 μm the absorption is weak and α L < 1. Where α is the absorption coefficient and L is the diffusion length of non-equilibrium carriers. In this case different recombination velocities at the front and rear detector surface are necessary in order to get good performance. Numerical results have been obtained for typical detector parameters.

Minority carriers lifetime measurements in CuInS 2 by photoelectromagnetic effect

Minority carrier lifetimes and surface recombination velocities have been measured in both n-and p-type CuInS 2 chalopyrite compounds, combining the photoelectromagnetic (PEM) effect and stationary photoconductivity (PC) effect. By using the experimental values of τ p and τ n we tried a valuation of the photovoltaic conversion efficiency for an ideal CuInS 2 homodiode.

PEM-effect in graded-gap semiconductor

The photoelectromagnetic (PEM) effect in graded-bandgap semiconductors has been discussed assuming position-dependent band parameters. The semiconductor sample was assumed to be relatively thick with a narrow carrier-excitation region and the equation describing the excess-carrier distributions as a function of position obtained. The excess carrier distributions in the PEM-effect configuration were computed for graded-gap epitaxial Cd βHg 1-βTe layers as an example.

Photoelectromagnetic effect in layered compounds

Photoconductivity (PC), photovoltaic and photoelectromagnetic (PEM) measurements are a very useful method for transport parameter investigation, particularly when the high resistivity of the materials makes difficult direct measurements. We have applied these effects to determine some transport parameters (τ,L) of the layered compounds GaSe, PbI2, HgI2 at room temperature. The experimental results have been compared with different theoretical models of phototransport suggested for anisotropic compounds.

Photoelectromagnetic effect in n-GaSe

Photoelectromagnetic (PEM) and photoconductivity (PC) measurements in n-type GaSe monocrystals are reported. The PEM and PC currents are calculated taking into account the anisotropy of the samples. From the analysis of spectral dependence the ambipolar diffusion parameters along the c axis are calculated. Estimates of lifetime and mobilities are also obtained.

Generalized Photoelectromagnetic Effect in Semiconductors

The photoelectromagnetic (PEM) response of high-purity single-crystal $n$-type InSb has been measured over the temperature range 80-300\ifmmode^\circ\else\textdegree\fi{}K. A comparison of the data with the results of a theoretical treatment of the PEM effect, generalized to include bulk generation at arbitrary magnetic field, gives values for the surface-recombination velocity on this material both as a function of temperature and of surface preparation. The results also include the first reported observation of a negative PEM response due to the diffusion of carriers into recombination sites at the illuminated sample surface.

High-Frequency Photoelectromagnetic Effect inp-Type InSb

The high-frequency response of the photoelectromagnetic (PEM) effect in $p$-type InSb has been studied both theoretically and experimentally over the temperature range 77-203 \ifmmode^\circ\else\textdegree\fi{}K. It was found that where the response curves could be characterized by a single time constant, the curves exhibited a high-frequency falloff with a 3-dB/octave slope, in contrast to the 6-dB/octave slope which was characteristic of the photoconductive (PC) response. At temperatures around 200 \ifmmode^\circ\else\textdegree\fi{}K, the same time constant entered into both the PEM and PC response. However, around 77 \ifmmode^\circ\else\textdegree\fi{}K, the PEM time constant was at least 3 orders of magnitude smaller than the PC time constant. This difference was shown theoretically to correspond to the difference between the steady-state electron and hole lifetimes, with which the PEM and PC time constants may, respectively, be identified. The character of the PEM frequency-response curves was found to change as the temperature was increased from 77 \ifmmode^\circ\else\textdegree\fi{}K, with evidence that more than one time constant was involved over the range 104-140 \ifmmode^\circ\else\textdegree\fi{}K. All the response curves observed experimentally can be quantitatively accounted for in terms of a two-independent-level recombination model with parameters which are only slightly different from those previously used by Hollis, Choo, and Heasell.