Thermal Emission Activation Energies Research Articles

Determination of capture barrier energy of the E-center in palladium Schottky barrier diodes of antimony-doped germanium by varying the pulse width

The capture barrier energy of the E-center deep level defect introduced in Pd/Sb-doped Ge by alpha-particle irradiation has been studied. Palladium Schottky barrier diodes (SBDs) fabricated by resistive evaporation technique were successfully characterised by current-voltage (I-V), capacitance-voltage (C-V), conventional and Laplace deep level transient spectroscopy. The rectification quality of Schottky contacts before and after irradiation was confirmed by I-V and C-V results. The ideality factor and doping density were determined to be in the range of 1.23 to 1.46 and 3.55 × 1015 to 5.25 × 1015 cm−3, respectively before and after irradiating the device with alpha-particles. The thermal emission activation energy and the apparent capture cross section of the E-center were determined from the Arrhenius plot to be 0.37 eV and 1.3 × 10−15 cm2, respectively. The capture barrier energyand the true capture cross section of the E-center were calculated to be 0.052 eV and 2.25 × 10−17 cm2, respectively from the experimental findings after varying the pulse width at different temperature range from 145 to 180 K in steps of 5 K.

DLTS studies of defects produced in n-type silicon by hydrogen implantation at low temperature

ABSTRACTMetastable defects are discovered in hydrogen-implanted n-type silicon. Hydrogen implantation was performed with the energy of 80 keV to a dose of 2×10 cm- at 109 K. After implantation, the sample temperature was raised to room temperature. DLTS measurements were carried out in the temperature range 80–290 K for fabricated diodes. When the sample is reverse-biased at 10V for 10 min at room temperature and then is cooled down to 80 K, three new peaks labeled EM1, EM2 and EM3 appear around 150, 190 and 240 K, respectively. The introduction of metastable defects is found to be characteristic of low temperature implantation. We have evaluated properties of EM1 in detail. EM1 with thermal emission activation energy of 0.29 eV has a peak in concentration around the depth of 0.64 μ m, which corresponds to the projected range of 80 keV hydrogen. EM1 is regenerated with the reverse bias applied around 270 K and is removed with the zero bias around 220 K.

New electron and hole traps in GaAsP alloy

Two electron traps and a hole trap have been observed in vapour phase epitaxial GaAs0.6P0.4 materials by deep level transient spectroscopy. The dominant electron trap A, which has never previously been reported, has a thermal emission activation energy of Ee A = 0.83 eV and an abnormally large capture activation e energy Ec A = 0.73 eV. Hole trap C with thermal emission activation energy of Ee C = 0.65 eV is also new and different from previous reports. A critical comparison of traps reported in this work with traps reported in the existing literature is also made.

Yellow Band and Deep levels in Undoped MOVPE GaN.

Undoped layers of GaN grown by MOVPE on sapphire substrates have been characterized by photoluminescence, photocapacitance and photoinduced current transient spectroscopy (PICTS). Photocapacitance reveals in all samples two specific signatures at photon energies of 1 eV and 2.5 eV. The photocapacitance decrease observed at 1 eV seems to be due to an electron capture process from the valence band, whereas the capacitance increase at 2.5 eV is related to an electron emission process. The fact that the capacitance step at 1 eV is only seen after photoionization at energies above 2.5 eV, and the observed correlation between its amplitude and the photoluminescence intensity of the “yellow band”, lead us to conclude that both transitions are linked to the same trap, which is also suggested to be responsible for the yellow band. The position of this trap, at 2.5 eV below the conduction band, is confirmed by PICTS measurements, that show a hole thermal emission activation energy of 0.9 eV at 350 K.

Properties of the deep donor states of AlxGa1−xAs:Se

A study of the electrical and optical properties of the Se deep donor states in AlxGa1−xAs:Se grown by metalorganic vapor phase epitaxy (MOVPE) process is reported. A novel experimental technique is presented to determine the absolute energy and the true density of the deep donor. The characteristics of the Se deep donor states are obtained from deep level transient spectroscopy, photoluminescence, photocapacitance, Hall effect measurements, isothermal capacitance transient measurements, and a quasistatic capacitance voltage technique. It is found that the Se dopant gives rise to at least two energy levels in the band gap. One is the generally observed deep donor level, commonly called the DX level and the other is a new shallower donor state which also exhibits DX-like properties. The concentration of the shallower state is less than 5% of the deep donor density. The densities of both donors increase with the mole fraction of H2Se used during MOVPE growth. Thermal emission activation energies of 0.29±0.01 and 0.24±0.01 eV were found for the deep and shallower donor states, respectively, for 0.23≤x≤0.41. The Se donor ionization energies relative to the Γ minimum are determined for samples with different AlAs mole fractions, and also, the true densities of Se donors are obtained. We propose a macroscopic model for the emission and capture mechanisms of Se donors in AlxGa1−xAs, which allows a consistent interpretation of the results obtained by different measurement techniques and provides a natural explanation for the low temperature Hall density saturation phenomenon and the persistent photoconductivity effect.

Effects of BCl3 magnetron ion etching on deep levels in GaAs

Capacitance versus voltage curves and deep-level transient spectroscopy have been used to investigate the effects of BCl3 magnetron ion etching on the shallow donor concentration and deep-level defects in GaAs. Capacitance versus voltage data reveal that the shallow donor concentration is unaffected by the etching process at power densities ranging from 0.08 to 0.4 W/cm2. Capacitance transient measurements reveal thermal emission of electrons from two deep defect sites with activation energies of 0.25 and 0.74 eV which were unaffected by the etching process. A broad, deep-level transient spectroscopy peak, characterized by an activation energy for thermal emission of electrons of 0.37 eV, was also observed in the etched sample, but not in the unetched sample. Defect depth profiling of the 0.37 eV peak indicates the concentration of this defect to increase with increasing etch power.

Study of Medium-Deep Traps in Undoped GaAs Grown by Arsenic-Pressure Controlled Cz Method

ABSTRACTProperties of medium-deep traps in n-type undoped GaAs crystals grown by arsenic-pressure controlled Czochralski (PCZ) method were studied by using capacitance transient spectroscopy (CTS) and temperature-dependent Hall (TDH) measurement. EL3 and EL6-like (EM2) traps were dominant medium-deep traps in D LTS measurements. The dependence of EM2 peak height on the duration of filling pulse and the detailed analysis of CTS showed that the trap EM2 spectrum consisted of three electron traps which had thermal emission activation energies of approximately 0.35 eV and various capture cross sections with activation energies for electron capture. On the other hand, the trap EL6 spectrum in n-type LEC GaAs was described by two levels of traps with activation energies of 0.32 eV and 0.33 eV for electron emission, respectively. It was concluded that so-called EL6 formed a family and some of its components were classified as defects with large lattice relaxation.

DX centers in AlAs and GaAs-AlAs selectively doped superlattices

Dx centers have been investigated using deep level transient spectroscopy (DLTS) in Si doped AlAs and in selectively doped GaAs-AlAs superlattices (SLS) grown by molecular beam epitaxy. The activation energy for thermal emission is E~ = 0.42 eV in both the SLS and AlAs layers. For the first time a study of the capture in a SL reveals a capture activation energy E~~ = 0.36 eV, which locates the Dx at E, m 60 mev below the conduction nfiniband. Taking into account the measured energies and trap concentrations, we show that the Dx observed in the SLS lies in the AlAs layers.

Characterization of D X centers in selectively doped GaAs-AlAs superlattices

Using deep level transient spectroscopy (DLTS), DX center has been characterized in GaAs-AlAs superlattices grown by molecular beam epitaxy and selectively Si-doped either in the AlAs layers or in the middle of the GaAs layers. The activation energy for thermal emission, which is the summation of the binding energy Et and the thermal capture energy Ec, is Ea=0.42 eV in both superlattices. The lowest DX concentration is obtained for the case where the only GaAs layers are doped. For the first time, a study of the capture reveals a capture activation energy Ec=0.36 eV, which locates the DX at Et≊60 meV below the conduction miniband. Taking into account the measured energies and trap concentrations, we show that the only observed DX on such structures is due to the silicon diffusion into AlAs layers.

Deep levels governing the transport mechanism in p-n HgMnTe diodes

Preliminary results of DLTS studies on Hg 1-xMn xTe ( x=0.18, 0.20) are presented. One dominant majority carrier trap on the p-type side of the diodes was observed. Its concentration, hole capture cross-section, and the activation energy for thermal emission were found to be equal to 5X10 16 cm -3, 10 -17 cm 2, and 110 meV, respectively. A strong dependence of defect occupancy on the number of electrons injected into the space charge region allowed us to identify these deffects as very effective recombination centers limiting the device performance.

DX centers in selectively Si-doped GaAsAlAs superlattices

DX center has been characterized in four GaAsAlAs superlattices grown by MBE at 580°C. The structures are uniformly Si-doped or selectively Si-doped in the AlAs layers or in the middle of the GaAs layers or on both sides of the interfaces. Deep level transient spectroscopy measurements (DLTS) put in evidence one dominant electron trap, with an activation energy for thermal emission of about 0.42eV for all the superlattices. This defect shows a thermally activated capture cross section and a large concentration except for the case where the only GaAs layers are doped. For the first time, a study of the capture reveals a capture activation energy of 0.36-0.37 eV, which allows us to locate the DX level nearly 60 meV below the conduction miniband. From these results, we show that the observed DX center is related to silicon in the AlAs layers. For the case when the AlAs barriers are not doped, the DX level is due to the Si diffusion from the middle of the wells towards the barriers, the Si atoms having diffused during the growth.

Novel method to determine capture cross-section activation energies by deep-level transient spectroscopy techniques

Deep-center characterization by deep-level transient spectroscopy (DLTS) allows a direct determination of the trap thermal emission activation energy. However, capture barrier energy measurements, based on trap partial filling by pulses of increasing width, require a quite different experimental processing and pose some hardware difficulties. In this letter we present a new method to determine the trap capture barrier energy, one that requires constant-width filling pulses and obtains capture information from standard DLTS data. This technique has been applied to Te-, Sn-, and Si-related DX centers in AlGaAs alloys.

Electron traps in GaAs0.6P0.4 p+n diodes fabricated by Zn implantation and rapid thermal annealing

Majority-carrier traps in p+n diodes fabricated by rapid thermal annealing (RTA) of Zn-implanted GaAs0.6P0.4:Te and in Schottky diodes fabricated on GaAs0.6P0.4:Te after only RTA were studied using deep-level transient spectroscopy (DLTS). RTA using halogen lamps was performed in the temperature range 830–1000 °C for approximately 6 s without any encapsulant. Two electron traps E1 and E2 were observed for both p+n and Schottky diodes and were found to have thermal emission activation energies of 0.20 and 0.36 eV, respectively. The broadened DLTS spectrum was observed and reproduced using the Gaussian distribution for thermal emission activation energies of these traps. Furthermore, traps E1 and E2 have thermal activation energies of 0.09 and 0.24 eV for electron capture, respectively. It is considered that these traps are native defects and may belong to donor-related (DX) centers. Depth profiles of shallow donors and traps were determined using capacitance-voltage measurements because of anomalously high concentrations of these traps. Shallow donor and trap concentrations were found to decrease over several μm from the surface for RTA Schottky diodes above ∼900 °C, but were observed to be uniform for RTA p+n diodes. The concentrations calculated for shallow donors and trap E2 by RTA at 1000 °C decreased exponentially with depth. The difference between p+n and Schottky diodes, and the possible mechanism for the decrease of shallow donor and trap concentrations by RTA are discussed. It is possible that the decrease of shallow donor and trap concentrations by RTA is due either to their interaction with vacancies produced near the surface or to their out-diffusion.

Photo-induced current transient spectroscopy for high-resistivity neutron-transmutation-doped silicon

Defects in high-resistivity neutron-transmutation-doped (NTD) silicon prior to annealing were studied by photo-induced current transient spectroscopy (PICTS). The thermal-neutron fluence was 9.5*1017 cm-2 to give a resistivity of about 30 Omega cm after annealing, and the fast-neutron fluence was 9.5*1016 cm-2. Four traps with thermal emission activation energies of 0.15, 0.41, 0.47 and 0.50 eV were observed in NTD silicon. A trap with a thermal emission activation energy of 0.15 eV was considered to correspond to a divacancy. Although the clustered nature of the defects was observed, PICTS measurements suggest that the material state of high-resistivity NTD silicon is still crystalline and not amorphous.

Optical Current DLTS with a Bipolar Rectangular Weighting Function for High-Resistivity Neutron Transmutation Doped Silicon

AbstractDefects in high-resistivity neutron transmutation doped (NTD) silicon without annealing were characterized by optical current DLTS with a bipolar rectangular weighting function using a GaAs LED. The DLTS method with a bipolar rectangular weighting function was also described. Two clear peaks labeled A and B were observed in addition to unresolved peaks due to overlaps of DLTS signals of several defects. The thermal emission activation energies of defects A and B were 0.15 and 0.50 eV, respectively. The DLTS signals of these defects were broader than the calculated ones. This indicates the clustered nature of defects produced by fast neutron irradiation. However, the fact that the characteristic peaks were observed suggests that the material state of high-resistivity NTD silicon is crystalline but not amorphous.

A DLTS study of electron irradiated InP

Samples of undoped, sulphur-doped, and germanium-doped InP have been irradiated with 2 meV electrons. Deep level transient spectroscopy was used to detect six electron traps and two hole traps introduced by the irradiation. Five of these are attributed to intrinsic defects alone, and the other three appear to be impurity related. The thermal emission activation energies and electron capture cross sections of the levels are reported. The results of thermal annealing experiments up to 300°C are discussed.

Deep levels introduced by electron irradiation of InP

Several InP samples have been irradiated with 2 MeV electrons. Six electron traps and two hole traps were detected by means of deep level transient spectroscopy (DLTS) and optical DLTS. One of these levels appears to have an unusually large lattice relaxation, having a small electron capture cross section, thermally activated with an energy of 0.33 eV. This is comparable to the thermal emission activation energy of 0.44 eV.

Electrical properties of platinum in silicon

The energy levels produced by platinum in silicon have been measured in p- and n-type material using deep-level transient spectroscopy and constant-capacitance thermal-emission-rate measurements. Within the sensitivity of the apparatus only two levels have been detected having thermal-emission activation energies of EC−ET=0.231 eV and ET−EV=0.321 eV. The majority-carrier capture cross sections of these levels have also been measured, giving σnA =7×10−15 cm2 and σpD=1.5×10−15 exp(−7.3 ×10−3/kT). Using these values together with thermal-emission data and assumed degeneracy factors of gA=0.5 and gD=2 in the equation of detailed balance, it was concluded that both levels were fixed to the conduction band edge.