PbTe／PbSnTe液相外延溶液

为了研究多元红外探测器响应波长均匀性,用PbTe/PbSnTe液相外延单相溶液进行了实验。本文论述了单相溶液的配比、结晶温度的测定、外延温度曲线、外延Pb_(1-x)Sn_xTe薄膜和溶液的分析以及用该溶液制备的PbTe/PbSnTe异质光伏16元红外探测器的性能。     

Calculation of the optimum vapor pressure for stoichiometry in PbTe and PbSnTe

Optimum vapor pressure for stoichiometry in growth of PbTe and PbSnTe has been calculated. The result is in a good agreement with the experimentally obtained ones for vapor pressure controlled Bridgman growth and liquid phase epitaxy. The procedure of calculation follows that performed earlier for GaAs, which assumed the equality of the chemical potentials of the volatile element in gas, liquid and solid phases. Also it is pointed out that the nonequilibrium reactions of interstitial Te atoms with Pb vacancies forming anti-site Te, as well as Te precipitations, take place at the highest applied Te vapor pressure region.     

Raman scattering in PbTe and PbSnTe films: In situ phase transformations

The PbTe and Pb_{1 ? x} Sn _x Te films, both undoped and doped with indium, are studied by Raman spectroscopy. It is found that the film surface changes during spectra recording. From comparative analysis of the data obtained in the study and those reported in publications, it is inferred that the 90, 117, and 138 cm^?1 peaks correspond to the scattering of light at tellurium or tellurium-oxide precipitates. It is established that these peaks appear in the spectra of Pb_{1 ? x} Sn _x Te films and epitaxial PbTe films only when doped with indium. The 180-cm^?1 peak is observed in the spectra of all of the samples and not attributed to the plasmon-phonon mode. The nature of the 180-cm^?1 peak is still not completely understood.     

Study on antireflective coatings of PbTe/PbSnTe heterojunction infrared detectors

ZnS antireflective coatings and passivation layer are developed on self-made PbTe/PbSnTe heterojunction infrared detectors and following experiments have been finished: WaterProof properties of ZnS coatings; Anti-reflective properties of PbSnTe materials and their detectors with ZnS coatings, respectively; ageing and stability tests of the PbSnTe detectors with ZnS coatings. All experimental results are excellent: The typical detectivity (D^*) of PbSnTe detector is 2.83×10¹⁰ cmHz^1/2W^?1. (with peak wavelength λp=9.8 μm and cut-off wavelength λc=11.7 μm). Average detectivity of the PbSnTe detector with ZnS anti-reflective coatings is increased by 45%. Ageing tests indicated that the PbSnTe detectors with ZnS coatings have still high stabilities after several years. They are used successfully in medical infrared imaging systems and other applications.     

Anomalous spectral response in heterojunction PbTe/PbSnTe infrared detectors—A new effect: Two peak effect

In the measurements of the spectral responses of PbTe/PbSnTe p-n heterojunction infrared detectors, we have discovered that there is a anomalous phenomenon in a few detectors when reverse bias is applied: there is not only a response peak in the 8–14 μm long-wavelength range, but also another response peak in the 3–6 μm short-wavelength range. We have also discovered that when reverse bias is increased, the heights of both spectral peaks can be adjusted, and the height of short-wavelength peak may be quickly increased, even if its long-wavelength peak is exceeded. This is a unreported new phenomenon up to now. It is shortly called “anomalous phenomenon”, or “Two Peak Effect” (TPE). This paper describes the new effect “TPE” firstly, and makes a theoretical explanation. On the basis of this effect, it would be passible to make a new type of IR detector, which is quite different from the available detectors.     

Lasing properties of PbSnTe/PbTe double hetero mid-infrared laser diodes grown by temperature difference method under controlled vapor pressure liquid-phase epitaxy

PbSnTe/PbTe double hetero-diode structures were grown by temperature difference method under controlled vapor pressure (TDM–CVP) liquid-phase epitaxy (LPE). These laser diode (LD) structures were of the PbTe (Bi)/Pb_1−xSn_xTe/PbTe (undoped substrate) double hetero (DH) type. The peak shift of the wavelength emitted by the fabricated diodes was recorded and it was found that they successfully lased from 15 K to over 77 K (liquid nitrogen temperature) at a slightly lower threshold current density than standard LPEs fabricated via the slow-cooling method. In addition, the lasing peak wavelength was longer than spontaneous emissions. The laser spectra of diodes with varying Sn concentrations (x) in the active layer were observed, and their intensities were recorded as a function of the wavelength. Very sharp lasing spectra were obtained between 6.5 μm and 9.4 μm (x=0–0.11), clarifying that the stoichiometry control possible with TDM–CVP is suitable for fabricating optical devices. In addition, it was demonstrated that TDM–CVP is appropriate for fabricating infrared optical devices constructed from Pb_xSn_1−xTe systems.     

Carrier recombination and deep levels in PbTe

The results of transient photoconductivity lifetime measurements and of impurity photoconductivity as well as Hall effect measurements obtained on PbTe films show that deep electron trapping levels exist in monocrystalline epitaxially grown PbTe. To our knowledge this is the first direct observation of deep levels in the gap of PbTe. The energetic position of the levels and their concentration were determined. The observed levels profoundly influenced the efficiency of PbTe infrared emitter diodes. This was shown experimentally by comparing the luminescence intensity of various diodes with different carrier concentration in the active zone. A strong decrease of luminescence intensity was observed for carrier concentrations greater than 10¹⁷ cm⁻³. This decrease could be explained by recombination via the observed levels in the gap.     

High field transport in PbTe

The drift velocity and Hall coefficient of tn and p-type PbTe at 77K were measured for various crystallographic directions of current up to field strengths of 1.5 kV/cm. Both the conductivity and the Hall effect are anisotropic with the latter depending also strongly on the magnetic field. These effects are attributed to nonuniform heating of the equivalent conduction band L-valleys of PbTe and equivalent intervalley transfer. For field strengths beyond 1 kV/cm oscillations of the current and the potential distribution occur. The Hall coefficient decreases sharply above this threshold indicating avalanche breakdown. At still higher field strengths a sign reversal of the Hall coefficient is observed. Probing the potential distribution, it could be shown that this instability is caused by high field domains, which travel along the sample with the drift velocity of the carriers. Possible mechanisms for the formation of high field domains are discussed.     

TE and TM coupling coefficients in distributed feedback double-heterostructure PbSnTe lasers

TE and TM coupling coefficients for double-heterostructure distributed feedback (DFB) Pb1-xSnxTe diode lasers are calculated. Results are presented for rectangular, sinusoidal, symmetric-triangular, and sawtooth gratings for both intermode and intramode coupling. Based on these results, the design considerations of PbSnTe DFB lasers are also discussed.     

Automatic network measurements in the time domain

The time-domain automatic network analyser (TDANA) is described. It utilizes time-domain measurements and the fast Fourier transform to obtain frequency-domain scattering parameters. A TDANA consists of a pulse generator, sampling oscilloscope, and a minicomputer. The present state of the art for TDANA's includes frequency coverage from dc to 18 GHz in a single instrument and complex scattering parameter measurement uncertainties of the order of 1 percent.     

Thermomagnetic Effects in High-Mobility PbTe Films

The narrow-gap compound semiconductor PbTe has high Hall mobility. The Fermi surface at the L-point in the Brillouin zone has large anisotropy. In this work, we measured thermomagnetic effects in PbTe thin films to confirm anisotropy of the Nernst coefficient A _Ne and show Nernst mobility from the ratio of A _Ne and the Seebeck coefficient S: μ _Ne = A _Ne/S. Angular dependences of the Nernst voltage show that A _Ne is independent of the angle between the temperature gradient and the magnetic field, because of the high L-point symmetry. The calculated Nernst mobility was compared with the Hall mobility. Because the former is smaller, the Mott equation cannot explain the Seebeck coefficient at room temperature.     

Minority carrier lifetimes and lasing thresholds of PbSnTe heterostructure lasers

A new calculation of radiative minority carrier lifetime in PbSnTe is presented which yields lifetimes an order of magnitude greater than previously accepted values. These results are used in combination with recent measurements of minority carrier lifetime and interface recombination velocity in PbSnTe double heterojunction laser structures to calculate DH laser thresholds. It is demonstrated that radiative recombination is a relatively inefficient process in present PbSnTe lasers, and that when this inefficiency is taken into account the magnitude of the experimentally observed threshold and its variation with active region width and temperature can be accurately predicted, even at low temperatures where all previous models have failed.     

Flow time measurements for underfills in flip-chip packaging

Flow time is a key material property for underfill materials in flip-chip applications. In this paper, we will discuss how to use flow time testing for underfill flow evaluation and material screening. The flow time of several underfills was measured at elevated temperatures using test pieces made from glass microscope slides. The material properties impacting underfill flow, such as viscosity, contact angle, and surface tension, were also experimentally measured and used to calculate estimated flow times using the Washburn equation. Empirical and calculated flow times were compared. The effects of channel width and flow distance on flow time were also studied. Additionally, the effect of a tilted stage on flow time, epoxy tongue, and void formation was evaluated.     

Oscillating transient currents in PbSnTe:In in a backgroundless mode

Damping oscillations of a current are found in the PbSTe:In films after supplying a direct voltage to them in the absence of background illumination. A nonmonotonic transition to the steady state is discussed in the scope of the theory of the currents confined by a space charge upon the capture of electrons injected from the contacts to the traps distributed by energy, which leads to oscillating variation in polarizability and injection current. The ratio of the total current under the excitation by laser radiation with wavelength λ = 205 μm (hν = 0.006 eV) to the dark current could be larger or smaller than unity depending on the injection level of the electrons, i.e., supplied voltage, which can be interpreted in the scope of the suggested model.     

Transit time and charge storage measurements in heavily doped emitters

We report results of a first direct measurement of the minority-carrier transit time in a transparent heavily doped emitter layer. The value was obtained by a high-frequency conductance method recently developed and used for low-doped Si. The transit time coupled with the steady-state current enables the determination of the quasi-static charge stored in the emitter and the quasi-static emitter capacitance. Using a transport model, we estimated, from the measured transit time, the value for the minority-carrier diffusion coefficient and mobility. The measurements were done using a heavily doped emitter of the Si p+-n-p bipolar transistor. The new result indicates that the position-averaged minority-carrier diffusion coefficients may be much smaller than the corresponding majority-carrier values for emitters having a concentration ranging from about 3 × 10¹⁹cm^-3to 10²⁰cm^-3.     

Donorlike behavior of rare-earth impurities in PbTe

The Hall coefficient, thermoelectric power, and electrical conductivity in PbTe doped with La, Pr, Sm, and Gd are investigated in the temperature range (77–700) K. The impurity atoms act as donors with an electrical activity that increases with temperature until the fraction of electrically active lanthanide atoms (Ln) reaches values close to or slightly more than half of their total number. A decrease in the electron mobility and a change in the thermoelectric power relative to their values in PbTe〈I〉 are also noted. At low temperatures, the Seebeck coefficient in PbTe〈Ln〉 is found to be higher than in PbTe〈I〉, while at high temperatures it is lower. The data are interpreted by invoking a band of impurity resonant states, whose energetic position and number are functions of composition and temperature. The experimental data imply that when La and Pr dope PbTe, the electrical activity of the compound is dominated by intrinsic donorlike defects that form when Ln is incorporated in the ratio LnTe. Fiz. Tekh. Poluprovodn. 32, 806–810 (July 1998)     

RF power transistor storage time: theory and measurements

Measurements on two types of UHF power transistors are given. The measured charge storage time constants (/spl tau//SUB s/) were 89 ns and 173 ns, effectively `infinite' for most applications. Then t/SUB s/ is essentially independent of /spl tau//SUB s/, and depends mainly on circuit properties: base drive and collector current waveforms. The measured dependence of t/SUB s/ on circuit and transistor parameters is in accordance with analytical predictions. Therefore storage time can be accounted for explicitly in a priori circuit design of RF power amplifiers.     

Sign-Alternating Photoconductivity in PbSnTe:In Films in the Space-Charge-Limited Current Regime

Semiconductors - The dependence of the photoconductivity sign on the bias voltage, intensity, and duration of illumination is studied for PbSnTe:In films in the space-charge-limited current regime....     

Coherence measurements with time sampling ocean-bottom seismometers

Instruments for obtaining simultaneous records of ocean-bottom seismic motion are described. Preliminary ocean-bottom seismic data with two simultaneous three-component instruments indicates that instrument noise and water currents may cause small differences in the detailed spectra. The general features of the spectra, however, appear to be the same from proximate instruments.