S.H. You

Origin of point defects in AgInS2/GaAs epilayer obtained from photoluminescence measurement

The AgInS2 epilayers with a chalcopyrite structure grown using a hot-wall epitaxy method have been confirmed to be a high quality crystal. From the optical absorption measurement, the temperature dependence of the energy band gap on AgInS2/GaAs was found to be Eg(T)=2.1365 eV−(9.89×10−3 eV)T2/(2930+T). After the as-grown AgInS2/GaAs was annealed in AgInS2/GaAs has been investigated by using the photoluminescence (PL) at 10 K. The native defects of VAg, VS, Agint, and Sint obtained from PL measurements were classified as a donors or acceptors type AgInS2/GaAs to an optical p type. Also, we confirmed that In in AgInS2/GaAs did not form the native defects because In in AgInS2 did exist in the form of stable bonds.

Point defects in p-type CdIn2Te4 Bridgman grown crystals

Abstract Single crystal of p-CdIn 2 Te 4 was grown in a three-stage vertical electric furnace by using Bridgman method. The quality of the grown crystal has been investigated by X-ray diffraction and photoluminescence (PL) measurements. From the PL spectra of the as-grown CdIn 2 Te 4 crystal and the various heat-treated crystals, the (D 0 , X) emission was found to be the dominant intensity in the PL spectrum of the CdIn 2 Te 4 :Cd, while the (A 0 , X) emission completely disappeared in the CdIn 2 Te 4 :Cd. However, the (A 0 , X) emission in the PL spectrum of the CdIn 2 Te 4 :Te was the dominant intensity like in the as-grown CdIn 2 Te 4 crystal. These results indicated that the (D 0 , X) is associated with V Te which acted as donor and that the (A 0 , X) emission is related to V Cd which acted as acceptor, respectively. The p-CdIn 2 Te 4 crystal was obviously found to be converted into n-type after annealing in Cd atmosphere. The origin of (D 0 , A 0 ) emission and its TO phonon replicas is related to the interaction between donors such as V Te or Cd int , and acceptors such as V Cd or Te int . Also, the In in the CdIn 2 Te 4 was confirmed not to form the native defects because it existed in a stable bonding form.

Band gap energy and valence band splitting of p-CdIn2Te4 crystal by photocurrent spectroscopy

Single crystals of p-CdIn2Te4 were grown by the Bridgman method without a seed crystal. From photocurrent measurements, it was found that three peaks, A, B, and C, correspond to the intrinsic transition from the valence band states of Γ7(A), Γ6(B), and Γ7(C) to the conduction band state of Γ6, respectively. The crystal field splitting and the spin orbit splitting were found to be 0.2360 and 0.1119 eV, respectively. The temperature dependence of the CdIn2Te4 band gap energy was given by Eg(T)=Eg(0)−(9.43×10−3)T2/(2676+T). The Eg(0) was calculated to be 1.4750, 1.7110, and 1.8229 eV at the valence band states of Γ7(A), Γ6(B), and Γ7(C), respectively. The band gap energy of p-CdIn2Te4 at room temperature was determined to be 1.2023 eV.

Point-defect study from low-temperature photoluminescence of CdGa2Se4 layers through the postannealing in various ambient

The CdGa2Se4 layers were grown by the hot-wall epitaxy method. From the absorption measurement, the band-gap variation in CdGa2Se4 was well interpreted using Varshni’s equation. After the postannealing in various ambient, the behavior of point defects in CdGa2Se4 was investigated by measuring photoluminescence (PL). Point defects originating from VCd, VSe, Cdint, and/or Seint were classified as donor or acceptor types. Thus, the Ga in CdGa2Se4 did not form native defects because the Ga existed in the form of stable bonds in CdGa2Se4. Based on these PL results, we schemed out a band diagram of the recombination process in CdGa2Se4.

Temperature-dependent study of photocurrent signal in CdGa2Se4 layers

The photoconductive CdGa2Se4 layer has been investigated using photocurrent (PC) spectroscopy as a function of temperature. Three peaks corresponding to the band-to-band transitions were observed in the PC spectra for all temperature ranges. From the relations of peak position and temperature, the temperature dependence of the band-gap energy is precisely discussed. Also, contrary to our expectation, the PC intensities decreased with decreasing temperatures. From the relation of log Jph versus 1/T, where Jph is the PC density, two dominant levels by the exponential variation in the PC with varying temperature were observed, one at high temperatures and the other at low temperatures.