Temperature Dependent Capture Cross Section Research Articles

Comparison of deep level spectra of MBE- and MOCVD-grown InGaAsN

AbstractDeep level transient spectroscopy (DLTS) studies of both p-type (uid) and n-type (Sidoped), lattice-matched, 1.05 eV bandgap InGaAsN grown by molecular-beam epitaxy (MBE) are reported, and the results are compared to previous measurements of similar materials grown by metal-organic chemical-vapor deposition (MOCVD). In MBE-grown p-type InGaAsN, two majority-carrier hole traps were observed: H3' (0.37 eV) and H4' (0.51 eV), and no evidence was found for the presence of minority-carrier electron traps. These two traps appear to be similar to two levels, H3 (0.48 eV) and H4 (0.5 eV), previously characterized in MOCVD-grown InGaAsN. In MBE-grown n-type InGaAsN, we observed a shallow distribution of electron levels, E1' (0 < EA < 0.35 eV), as well as a deep electron trap E4' (0.56 eV) and a deep hole trap H5' (0.71 eV). E1' appears to be coincident with a superposition of two levels observed in MOCVD-grown InGaAsN, a shallow distribution termed E1 (0 < EA < 0.20 eV) and a discrete (though broadened) level E3 (0.34 eV). Further, E4' appears to be similar in character to a level observed in MOCVD-grown material, E4 (0.82 eV), although a disparity in activation energy exists. This disparity may be due to a temperature-dependent capture cross-section for one or both levels, a possibility that is currently under investigation. In contrast, H5' appears to have no analogue in MOCVD-grown material and thus may be unique to the MBE growth technique.

Characteristics of electron traps in Si-doped Ga 0.51In 0.49P and electrical properties of modulation doped GaInP/InGaAs/GaAs heterostructures

In order to investigate the feasibility of Si-doped Ga 0.51In 0.49P for modulation-doped field effect transistor applications, single Ga 0.51In 0.49P layers and Ga 0.51In 0.49P/In x Ga 1− x As/GaAs ( x=0,0.15 and 0.25) modulation doped heterostructures grown by gas source molecular beam epitaxy were characterized through deep level transient spectroscopy and Hall-effect measurements. Electrical characterization of the undoped and moderately Si-doped ( N D =3×10 17 cm −3 ) GaInP layers yielded an electron trap with an activation energy of 0.75 eV and a temperature dependent capture cross section with a capture barrier of 0.593 eV. The density of this trap increased, and an anomalous decrease in the free carrier concentration of GaInP was observed after the samples were annealed at temperatures typically used in device processing. While, this trap showed characteristics similar to DX centers, it was not detected in highly Si doped ( N D ≈4×10 18 cm −3 ) as grown layers suggesting that the trap is a defect complex including a residual impurity. While very high two-dimensional electron gas density ( 2.6×10 12 cm −2 at 30 K) was achieved in the lattice matched ( x=0) structures, the strained structures were found to be very sensitive to heat treatment, although the InGaAs layers thicknesses were below the theoretical critical thickness. Persistent photoconductivity and a significant reduction in the interface sheet electron density were observed after annealing. The anomalous behavior can be attributed to the decrease in the carrier concentration of the doped GaInP barrier layer and to the strain relaxation at the hetero-interface after annealing. While other explanations may be possible, the decrease in the GaInP electron concentration can be attributed to Si atoms moving from donor to acceptor sites.

Measurement of the Temperature Dependence of Silicon Recombination Lifetimes

AbstractLifetime spectroscopy is a valuable tool in a number of silicon-based technologies. Currently, lifetime measurement is the most sensitive diagnostic for identification of lowlevel metal impurities in silicon by using the ratio of high-injection to low-injection lifetime. When a single impurity dominates recombination, the lifetime as a function of injection level provides a measure of the defect concentration. Another measurement parameter, that has not been commonly used, is the lifetime as a function of temperature. Temperaturedependent lifetime analysis leads to a better understanding of trapping-delayed recombination rates, trapping and recombination center energy levels and activation energies, temperaturedependent capture cross sections, and surface or grain boundary recombination or trapping effects. A contactless measurement technique has been developed that provides the sample's recombination lifetime over a temperature range from 80 K to 300 K. A sample is coupled to the measurement circuitry that is placed into a Dewar where it is cooled by liquid nitrogen. Lifetimes are then measured as the sample is allowed to warm to room temperature. Data will be shown on these variable-temperature lifetime measurements, which have been made on silicon wafer material ranging from high-quality float-zone-grown wafers to low-cost polycrystalline materials used in photovoltaics.

Does the low-temperature Arrhenius plot of the photoluminescence intensity in CdTe point towards an erroneous activation energy?

Several experimental photoluminescence (PL) bands of different energies for variously prepared CdTe samples are compared. Temperature variation of the PL intensity is modeled with two nonradiative thermal activation energies, of which ET1 is dominant for about T⩽60 K, and ET2 for the upper temperature range of the measurement. The size of ET1 is invariably of the order of a few meV and, although of unclear origin, its magnitude is usually interpreted as an electronic energy level difference over which the carriers escape by thermal excitation. In CdTe the existence of such a small energy level difference ET1 is not easy to explain. On the contrary, we find clear evidence that, at low temperature, the PL intensity reduction with increasing temperature in fact results from the approximately T−2 temperature dependent capture cross sections of the carriers at the recombination centers, and not from a genuine thermal activation energy ET1.

On the thermally stimulated conductivity with small recapture rate and temperature dependent capture cross sections

Thermally stimulated conductivity (TSC) peaks corresponding to small recapture rate and temperature dependent capture cross sections are investigated. The shape of the TSC peak is studied by computing the shape factor μg (x) not only at the fractional intensity x = 1/2 as done conventionally but also at x = 2/3 and 4/5. It is found that for a particular value of x, μg(x) depends on um = E/kTm (E = activation energy, k = Boltzmann’s constant, Tm = peak temperature). A set of expressions based on the shape of the peak has been derived, which in principle can be used to evaluate the activation energy of such TSC peaks. The applicability of those expressions has been tested by considering some numerically computed and experimental TSC peaks.

DX-like centre in bulk GaSb:S

Hall, conductance, capacitance transients and DLTS measurements were carried out on Czochralski grown GaSb doped with sulphur. A deep centre with a small and temperature dependent capture cross section and with a high concentration was observed. Such features together with the detected persistent photoconductivity indicate that the observed centre is sulphur related DX-like centre. Some properties of the centre are presented and discussed.

Analysis of Anomalous Peak Heights in DlTS of MBE-Grown Aluminum Gallium Arsenide

ABSTRACTDLTS data taken on MBE grown AlGaAs films show peak heights which increase, maximize, and then decrease with increasing sample temperature. This behavior is difficult to explain within the context of conventional DLTS analysis. We suggest that the data can be accounted for by a trap with a temperature dependent capture cross section in conjunction with a model described by Lee and Borrego in which electron and hole emission rates are comparable. Using this analysis, we obtain an effective trap depth Eeff of 0.35 eV and a capture cross section activation energy Eσ 0.25 eV.

A Localized Defect in InP with Strong Temperature Dependence of Capture Cross-Section

The properties of the localized deep-level MOE2 in InP have been investigated. The electron capture cross-section has a strong temperature dependence in the temperature range from 222 K to 276 K. A thermal depth of Et=0.15 eV and an optical depth of Eopt=0.48 eV have been obtained for MOE2 by normal and optical deep-level transient spectroscopy (DLTS). These results indicate that a Stokes shift, which is characteristic of strong electron-phonon coupling, occurs at the MOE2 level. The experimental results on the temperature-dependent capture cross-section can be explained fairly well by the recently-formulated multiphonon emission electron capture mechanism.

Thermally Stimulated Emission and Conductivity Peaks in the Case of Temperature Dependent Trapping Cross Sections

The original theory of thermally stimulated emission is extended to include the effect of a temperature dependent trapping cross section. A method is proposed whereby the ionization energy and temperature dependent capture cross section of a set of identical trapping states may be determined from the half-width and shape of a thermally stimulated emission peak obtained from a single experiment. The method is also applicable to thermally stimulated current peaks if the free electron lifetime varies only slowly with temperature.

Temperature Dependence of Electron-Bombardment-Induced Conductivity in MgO. II

Previous measurements of the temperature dependence of the electrical conductivity induced in single crystals of MgO by bombardment with 1.3-Mev electrons over the temperature range 290\ifmmode^\circ\else\textdegree\fi{}K-600\ifmmode^\circ\else\textdegree\fi{}K have been extended to 100\ifmmode^\circ\else\textdegree\fi{}K. Two crystals from different sources were investigated.The bombardment-induced current, ${I}_{c}$, varies linearly with primary current, ${I}_{p}$, at 298\ifmmode^\circ\else\textdegree\fi{}K and at 105\ifmmode^\circ\else\textdegree\fi{}K. However, in certain cases measurements of ${I}_{c}$ vs applied voltage, ${V}_{c}$, reveal a deviation from Ohmic behavior which is enhanced at low temperature.The bombardment-induced conductivity exhibits a maximum near 250\ifmmode^\circ\else\textdegree\fi{}K. Both crystals display a temperature dependence at low temperatures which is consistent with the power-law relationship $\frac{{I}_{c}}{{I}_{p}}=k{T}^{m}$, where $m=3.3 \mathrm{and} 3.8$, respectively.A rising non-Ohmic ${I}_{c}$ vs ${V}_{c}$ characteristic appears to be dependent upon the magnitude of the applied field, the onset occurring at 3\ifmmode\times\else\texttimes\fi{}${10}^{4}$ v/cm. Collision ionization and warm carrier phenomena, rather than surface effects, probably account for the observed results.It is impossible to ascribe the temperature dependence of the bombardment-induced conductivity solely to the temperature variation of the carrier mobility. The results can be explained in terms of change with temperature of both the lifetime and mobility of the charge carriers. A combination of optical mode (polaron), acoustical mode, and ionized impurity scattering is assumed, in addition to a temperature-dependent capture cross section for the carrier. The theoretical curve fits the experimental data satisfactorily, and gives reasonable values for the parameters.