Thermoelectric Effect Spectroscopy Research Articles

Thermoelectric effect spectroscopy measurements on semi-insulating GaN

A simplified setup for thermoelectric effect spectroscopy (TEES) was introduced. This was applied for measurements on semi-insulating GaN, grown on a sapphire substrate in order to investigate deep level traps. TEES currents were found to be negative at lower temperatures and positive at higher temperatures, indicating that shallower levels belong to electron traps, and deeper levels to hole traps. Traps were fully characterized by using the thermally stimulated current measurements and the simultaneous multiple peak analysis method. The shallowest observed electron and hole traps have activation energies E C −0.09 eV and E V +0.167 eV, respectively. The possible microscopic origin of analyzed defects was discussed.

Thermoelectric effect spectroscopy of deep levels in semi-insulating GaN

The report of thermoelectric effect spectroscopy (TEES) applied on semi-insulating GaN was presented. The type of TEES setup, especially suitable for film-on-substrate samples, was devised. TEES enabled determination of sign of observed deep traps. Using TEES and thermally stimulated current spectroscopy measurements in combination with the simultaneous multiple peak analysis formalism all important trap parameters were determined. The shallowest identified electron and hole traps had activation energies Ec−0.09 eV and Ev+0.167 eV, respectively. Results indicate that both these traps, oppositely charged are present in the studied material in relatively high concentrations causing the electrical compensation and high resistivity.

Electrical compensation in CdTe andCd0.9Zn0.1Teby intrinsic defects

The effects of two intrinsic deep levels on electrical compensation in semi-insulating CdTe and Cd-Zn-Te crystals are reported here. These levels were found in samples grown by conventional Bridgman and high-pressure Bridgman techniques. The levels were observed with thermoelectric effect spectroscopy at distinct temperatures corresponding to thermal ionization energies of ${E}_{d1}{=E}_{v}+0.735\ifmmode\pm\else\textpm\fi{}0.005\mathrm{eV}$ and ${E}_{d2}{=E}_{v}+0.743\ifmmode\pm\else\textpm\fi{}0.005\mathrm{eV}.$ The first level is associated with the doubly ionized Cd vacancy acceptor and the second level was tentatively identified as the Te antisite $({\mathrm{Te}}_{\mathrm{Cd}}),$ which is thought to be complexed with a vacancy. The second level was found to electrically compensate CdTe and Cd-Zn-Te to produce high resistivity crystals, provided that the Cd vacancy concentration is sufficiently reduced during crystal growth or by post-growth thermal processing.

Influence of deep levels on CdZnTe nuclear detectors

We report deep level characterization on CdZnTe nuclear detectors grown by the high pressure Bridgman method. Three CdZnTe samples taken from the top, middle and tail of the same ingot were investigated using photo-induced current transient spectroscopy and thermoelectric-effect spectroscopy. Three major traps are detected and their influence on the nuclear detection properties are discussed.

Low Temperature Photoluminescence and Photoinduced Current Spectroscopy on CdZnTe Grown by High-Pressure Bridgman Technique

AbstractLow temperature photoluminescence (PL), photoinduced current spectroscopy (PICTS) and thermoelectric effect spectroscopy (TEES) measurements have been carried out on several CdZnTe samples, taken from the same ingot, grown by the High Pressure Bridgman Technique. The PL bandgap edge luminescence allowed us to study the quality of the CdZnTe material. We have also determined the zinc segregation through the ingot. A broad luminescence band at lower energies was observed and correlated with PICTS results. The behavior of the defects through the ingot was studied by PICTS. Finally, these results are used to implement the resistivity model.

Trapping properties of cadmium vacancies inCd1−xZnxTe

The trapping and thermal emission of holes were studied from a deep acceptor level created during thermal annealing of a ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Zn}}_{\mathrm{x}}$Te (x=0.12) crystal grown by the high-pressure Bridgman (HPB) technique using thermoelectric-effect spectroscopy and thermally stimulated current experiments. The deep level, which is usually absent in as-grown HPB ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Zn}}_{\mathrm{x}}$Te crystals, is assigned to the 2-/- acceptor level of Cd (Zn) vacancies. The thermal ionization energy of the level is ${\mathrm{E}}_{\mathrm{th}}$ =(0.43\ifmmode\pm\else\textpm\fi{}0.01) eV, and the trapping cross section of holes was found to be \ensuremath{\sigma}=(2.0\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}16}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$.

Deep electronic levels in high-pressure Bridgman Cd 1− xZn xTe

The behavior of deep electronic levels was studied as a function of Zn concentration in CdZnTe crystals grown by the high-pressure Bridgman technique using thermoelectric effect spectroscopy. A significant increase of the thermal ionization energies of hole traps was observed with the increasing Zn content of the ternary compound. The effect explains the stronger hole trapping and the resulting much shorter hole lifetime usually observed in CdZnTe as compared to CdTe. The behavior also suggests increased carrier recombination and explains the strong deterioration of electron collection in detectors fabricated from CdZnTe of high Zn concentration.

Role of cadmium vacancy-related defects in CdTe nuclear detectors

We report on the deep level which is responsible for the degrading performance of CdTe nuclear detectors. Three CdTe wafers, undoped, Al-doped, and Zn-alloyed (Zn = 10%), prepared by high pressure Bridgman technique were investigated using thermo-electric effect spectroscopy. The cadmium vacancy (V Cd)-related defects, behaving as electron trap at E C − 0.73 eV, was found to be responsible for the degrading performance of the detectors. The best detector was found to be from the material with the lowest concentration of this defect. This electron trap acts as hole recombination center, decreasing the hole collection efficiency in the photocurrent measurement. A V Cd-related hole trap, at E V + 0.21 eV, was also observed in these samples. We suggest that alloying with zinc could be effective in eliminating these V Cd-related deep levels, and hence improving the detector performance.

A simple and reliable method of thermoelectic effect spectroscopy for semi-insulating III-V semiconductors

We have developed a simpler and more reliable method of thermoelectric effect spectroscopy (TEES), eliminating the second heater in the technique. We have applied this method to the deep level studies in the semi-insulating undoped or Cr-doped GaAs materials and in the GaAs epitaxial layers grown at a low temperature by molecular beam epitaxy. We have found that the electrical contacts made on front and back surfaces of the sample are more reliable for the TEES measurement than both contacts made on the same surface. In this contact arrangement, the temperature difference of about 1–2 K between the back and front surfaces is enough to produce a clear and reliable TEES data, without the need for a second heater. The results obtained by TEES are consistent with the results obtained by photoinduced transient spectroscopy (PITS) and by thermally stimulated current (TSC) measurements. The TEES results clearly distinguish between the electron traps and the hole traps. We discuss the results on the various semi-insulating GaAs samples and the advantages and limitations of the TEES technique.

Deep level studies in MBE GaAs grown at low temperature

The photo-induced current transient spectroscopy (PICTS), thermoelectric effect spectroscopy (TEES) and thermally stimulated current (TSC) spectroscopy have been used to characterize the deep levels in the GaAs materials grown at low temperature by molecular beam epitaxy. At least five hole traps and five electron traps have been identified by the TEES measurement employing a simplified sample arrangement. We have studied the behavior of various traps as a function of the growth temperature and the post-growth annealing temperature. Some of the shallower hole traps were annealed out above 650‡ C. Electron traps atE c- 0.29 eV andE c- 0.49 eV were present in the material, and have been identified as M3 and M4, respectively. The dominant electron trap, atE c- 0.57 eV, is believed to be associated with the stoichiometric defect caused by the excess As in the material, and our data show evidence of forming a defect band by this trap. A possible model involving As precipitates is proposed for this trap atE c-0.57 eV.

Study of Deep Levels in LT-GaAs Materials and SI-GaAs Wafers by an Improved Thermoelectric Effect Spectroscopy

ABSTRACTWe have developed a simpler and more reliable method of thermoelectric effect spectroscopy (TEES) by eliminating the second heater in the technique. We have applied this method to the deep level studies in semi-insulating(SI) GaAs epitaxial layers grown at a low temperature by molecular beam epitaxy (LT-GaAs) and SI-undoped GaAs, Cr-doped GaAs. We have found that the electrical contacts on front and back surfaces of the sample are more reliable for the TEES measurement than both contacts made on the same surface. In this contact arrangement, the temperature difference of about 1–2K between the back and front surfaces was enough to produce a clear and reliable TEES data, without the need for a second heater. The results obtained by TEES are consistent with the results obtained by photo-induced current transient spectroscopy (PICTS) and by thermally stimulated current (TSC) measurements. The TEES results clearly distinguish between the electron traps and the hole traps. We will discuss the results on the various semi-insulating GaAs samples and the advantages and limitations of the TEES technique.

Thermoelectric effect spectroscopy of deep levels—application to semi-insulating GaAs

A new method, thermoelectric effect spectroscopy, is proposed for the analysis of deep levels in semi-insulating materials. Besides the information on energy position and relative concentrations of traps, the main advantage of the method is its ability to determine the trap sign, i.e., the method is capable to resolve electron traps from hole traps. The proposed method is very simple for application. It is also shown how in combination with other techniques it can give a complete picture about trap-filling dynamics during low-temperature transient phenomena caused by illumination. The applicability and validity of the method are demonstrated on GaAs in which both electrons and hole traps are found.