T. I. Galkina

Bolometric detector embedded in a polycrystalline diamond grown by chemical vapor deposition

A fast bolometric detector embedded in a plate of chemical-vapor-deposited polycrystalline diamond was developed and fabricated. The working element of the bolometer is a buried graphitized layer (with temperature-sensitive resistance) fabricated in the bulk of a diamond by C+ ion implantation followed by annealing. The kinetics of the response of the structure to irradiation with light from an LGI-21 pulsed nitrogen laser (λ = 337 nm, τP ∼ 8 ns) were studied. The room-temperature response width at half-maximum is ∼ 20 ns. Using the space-time distribution of responses of the structure, thermal (bolometric) signals were resolved from signals of different nature (photoconductivity or photovoltage).

Thermal parameters of layers and interfaces in silicon-on-diamond structures

The heat propagation at room temperature was studied in a heterostructure consisting of a polycrystalline diamond film deposited from a hydrocarbon plasma on an oriented silicon substrate. The dynamics of cooling of a thin-film indium thermometer evaporated atop the diamond film was measured following its heating by nanosecond nitrogen laser pulses. The experimental data were compared with the values calculated in the framework of the theory of thermal conductivity for multilayer systems. This analysis permitted the determination of both the thermal conductivity of the diamond film and the thermal resistance of the diamond/Si and In/diamond interfaces.

Propagation of acoustic phonons across the interfaces in CdTe and Si/CVD-diamond and quasi-two-dimensional phonon wind in CdTe/ZnTe quantum wells

Using a heat-pulse technique we investigated propagation of acoustic phonons in twinned CdTe, ZnTe crystals, in the vicinity of CdTe/ZnTe quantum well, and Si/CVD-diamond structures. Phonon mean free paths in CdTe were estimated. We studied the effect of phonon wind on the luminescence of narrow CdTe quantum well and observed an increase in the total luminescence intensity and the change of the luminescence band shape. We believe that this effect is due to a quasi-two-dimensional lateral propagation of subsurface and interface acoustic phonons in the ZnTe/CdTe structure. Preliminary data obtained on the Si/CVD-diamond interfaces suggest they are strongly damaged. To reduce the thermal boundary resistance of the interface between the material studied and the thin-film phonon detector we developed a buried bolometer based on a graphitized layer produced by ion implantation in diamond.

Unsteady-state heart transfer in stoichiometric cadmium telluride at low temperatures and laser excitation

The heat-pulse technique was employed to study the heat transfer in laser-pulse excitation in a high-purity grain-oriented CdTe growth by multiple sublimation. Comparison of the heat pulses obtained in the experiment with the results of calculations by the Monte Carlo method allowed one to evaluate the mean free path of the acoustic phonons in this material. It is proposed on the basis of the results obtained that the scattering by planar defects (grain boundaries and twinning planes) is the main mechanism of phonon scattering at low temperatures.

Heat pulse propagation in Si substrates after YBCO laser ablation

Abstract The propagation of heat pulses produced in thin silicon wafers by photoexcitation is investigated before and after the YBCO laser ablation. The Monte-Carlo simulation and analysis of the heat pulse shape led to conclusion about the introducing into the Si substrate of the acceptor type additional centers in the process of laser ablation. These centers turn to be phonon scatterers and therefore change the heat transfer velocity.

The measurement of the temperature inside the hot phonon spot induced by laser excitation of silicon

Abstract The heat pulses produced by laser excitation were measured in Si using YBCO sensor. The observed pulse shapes confirm the existence of the phonon hot spot in certain experimental conditions. The exploiting of YBCO bolometer and rather thin Si sample allowed the direct measurement of the hot spot temperature and its life time. Measured hot spot parameters are in satisfactory agreement with those obtained by help of Kazakovtsev-Levinson theory. The Monte-Carlo simulation of phonon propagation was carried out with account of coalescence process. It was found that with increase of excitation energy density, the calculated response peak position shifts noticeably to greater time values.

Propagation of nonequilibrium phonons in single-crystal ZnTe

Propagation of nonequilibrium acoustic phonons in ZnTe single crystals at helium temperature was studied with phonons being both optically generated and produced by a metal-film heater. Experiments with [110] ZnTe allowed for the detection of the arrival of longitudinal and transverse acoustic phonons, which are particularly well resolved when generated by a heated metal film. A bolometer also detected emission of ZnTe material with a time constant τ ∼ 90 ns, which can apparently be attributed to the luminescence of oxygen complexes, because the lifetimes of other complexes and bound excitons are substantially shorter.

Nonequilibrium phonon propagation in high-purity CdTe

Propagation of nonequilibrium acoustic phonons in samples of high-purity CdTe (impurity content ∼1016 cm−3) was studied using the heat pulse technique under pulsed photoexcitation. An analysis of nonequilibrium phonon propagation made by comparing the experimental response with Monte Carlo calculations assuming samples to be without twins provided an estimate for the spontaneous anharmonic phonon decay constant AL=2×10−52 s−1 Hz−5. The probability of free phonon transit through a twin boundary in a sample with twin structure was estimated as AC=0.96.

Propagation of nonequilibrium acoustic phonons in high-purity coarse-grained ZnTe

Propagation of nonequilibrium acoustic phonons in coarse-grained ZnTe obtained through vacuum sublimation was studied using the heat pulse method under both optical and metallic-heater phonon generation. The phonon mean free paths in the samples studied were shown to be 14 µm and to be dominated by scattering from twin boundaries.

A bolometric detector built into the diamond bulk

Since diamond can be used as both the substrate and the active medium in electronic devices, it is very important to obtain information concerning the temperature variations in the immediate vicinity of active elements and the conditions of heat removal from such elements. This task is solved by a bolometer built into a diamond plate, which is capable of measuring temperature increments induced by laser pulses in the diamond or in the diamond-supported surface structures. The bolometer, representing a buried graphitized layer formed by helium ion implantation with subsequent annealing, has a characteristic response time of ∼10 ns.