Iodine Chemical Transport Research Articles

Investigation of electronic properties of gallium sulfide single crystals grown by iodine chemical transport

Photoinduced-current-transient-spectroscopy and space-charge-limited-current measurements have been performed on n-type GaS single crystals grown from vapor by iodine chemical transport. Three electron traps located at 0.17, 0.45, and 0.56 eV from the conduction band have been detected, with a thermal capture cross section of 2×10−19, 5×10−14, and 8×10−13 cm2, respectively. Moreover, by Hall-effect measurements, an impurity hopping conduction with an activation energy of 0.12 eV has been evidenced in the range of temperatures between 220 and 320 K.

Deep levels in zinc phosphide

Deep majority-carrier traps have been studied by means of deep level transient spectroscopy (DLTS) in as-grown Zn3P2 polycrystals (p-type) grown either by sublimation or by iodine chemical transport using an automated digital DLTS system. Three main deep hole traps are present in both kinds of Zn3P2: hole traps with activation energy of 0.20±0.01 eV 0.36±0.005 eV, and 0.73±0.01 eV from the top of the valence band. In a few sublimation-grown samples a 0.48±0.02 eV hole trap is detected. The concentration of these levels, however, exhibits a very strong dependence on the thermal history of the samples, since Mg from the Schottky contact easily diffuses into the bulk above 50 °C and affects the concentration of the levels.

Radiative recombination and shallow centers in CuInSe2

The cathodoluminescence of single crystals of CuInSe2 obtained by melt-grown and iodine chemical transport was studied. As-grown crystals and crystals annealed in Se, In, or in a vacuum were used. We show the emission intensity decreases when the conductivity changes from n to p and then increases due to the decrease of the number of donors created by Se vacancies. We also show that two donor levels (60 and 80 meV) are introduced by the Se vacancy probably associated with impurities, and that the cation (probably Cu) vacancy causes an acceptor level at 40 meV. Another acceptor level is also determined, having a binding energy ≳80 meV.

Pair transitions in Zn3P2

Laser-excited photoluminescence emission has been measured from 2.5 to 100 °K for single crystals of Zn3P2 grown either by sublimation or by iodine chemical transport. Sublimation-grown crystals show two main peaks at 1.361 and 1.354 eV at 2.5 °K, each of which has a phonon replica displaced by 43 meV, and a third much smaller peak observable only above 20 °K at 1.367 eV. Iodine-transport grown crystals show a broad peak at 2.5 °K at 1.320 eV and its phonon replica displaced by 42 meV. The photon energy for peak emission shifts with excitation intensity as is typical of pair transitions, for the major bands seen at 2.5 °K. Temperature dependence measurements identify the donor and acceptor ionization energies corresponding to each of these bands.

Single crystal growth of Zn3P2

A closed-tube horizontal vapor transport system has been used for the growth of large single crystals of Zn3P2. Crystals were grown both with and without iodine chemical transport. The temperature profiles used and growth rate variations are described. When low concentrations of iodine on the order of 5–10 mg/cm3 were used an enhancement in growth rate was found, whereas a reduction in growth rate was found for larger iodine concentrations on the order of 25 mg/cm3. The dimensions of the largely single crystals were 1.2 cm in diameter and 4 cm long. The as-grown resistivities for the crystals grown by both techniques were on the order of 50 Ω cm.

Donor-acceptor pair transitions in CuInS2

We have studied the cathodoluminescence (edge emission) of single crystals of CuInS2 obtained by iodine chemical transport. Emission intensity as a function of excitation, temperature, and time [time resolved spectroscopy] allow us to reveal donor-acceptor transitions. By fitting the TRS spectra, we calculate the ionization energy of the impurities involved: EA,D≃45 meV, ED,A ≃95 meV, as well as the maximum transition probability: WMAX≃108 s−1.

Luminescence and lattice defects in Cu In S 2

We have studied the cathodoluminescence of single crystals of Cu In S 2 obtained by iodine chemical transport. As grown crystals and crystals annealed in In, S, (In + S), or in vacuum, were used. Two types of spectrum were observed, one for n type crystals due to S vacancies, and the other for p type or compensated crystals, which is interpreted as donor-acceptor pair transitions (determined by Time Resolved Speetroscopy) between the S vacancy (donor ~90 meV) and the Cu vacancy (acceptor ~45 meV), and by the corresponding free-to-bound transitions.

Vapour phase chemical transport properties of the cadmium telluride-iodine system

The vapour phase chemical transport properties of the CdTe : I2 system have been investigated. By comparing the experimental transport rate with the theoretical transport rate calculated on the basis of a three reaction transport model, it was shown that no iodine chemical transport is possible in closed tubes in the hot-cold direction, but only vapour phase transport controlled by the source sublimation. Thin platelets with large smooth surfaces were observed growing on the source charge under small temperature gradients. Their growth was explained in terms of a reverse (cold-hot) iodine transport associated with a reduced sublimation tendency of the facetted crystallized material with respect to the unfacetted powdered material of the charge.

Single crystals and epitaxial films of ZnSe by chemical transport

Single crystals of ZnSe up to 2 cm in length have been grown by iodine chemical transport with a 3–5°C thermal gradient. Dopants were introduced uniformly by this growth technique. Nonhomogeneous crystals of Zn(S, Se) were obtained by this method. Epitaxial growth of ZnSe on GaAs substrates by HBr transport was studied for various orientations. Use of excess Zn during deposition produced films having mobilities greater than 1000 cm 2/V-sec.