Colloidal Cu₂Zn(Sn_1−xGe_x)S₄nanocrystals: electrical properties and comparison between their wurtzite and kesterite structures

Abstract

Wurtzite colloidal Cu 2 Zn(Sn 1Àx Ge x )S 4 nanocrystals with a nearly monodispersed size distribution and tunable compositions were prepared. The optical band gaps linearly tune from 1.57 to 2.13 eV as the parameter x increases from 0 to 1. Kesterite nanocrystals were also obtained by replacing thiourea with sulfur powder. Enhanced zinc content accompanied with increasing germanium (Ge) incorporation is found for both hexagonal and tetragonal crystalline samples. The electrical properties of the multinary compounds indicate a decline in dark current density as the Ge content rises; however, the maximum illuminated current density comes from the sample with a Ge/(Ge + Sn) ratio of 0.28. The higher dark and illuminated current densities, as well as higher photon current/dark current ratios observed in nanocrystals with a wurtzite structure were further demonstrated by a comparison with the properties of kesterite compounds.

Wide band-gap tuning Cu2ZnSn1−xGexS4 single crystals: Optical and vibrational properties

“…The application of the multiwavelength excitation methodology described by Dimitrievska et al [41] based on the simultaneous fitting of the Raman spectra obtained under resonant, and non-resonant conditions (325, 532 and 785 nm excitation wavelengths) allows determining the characteristic peaks of CZTS, CZT 0.5 G 0.5 S and CZGS samples. The comparison of the peak positions reported for kesterite [41,42], wurzite [43], and wurtztannite [44] crystal structures allows identifying the structure of the CZTGS system as kesterite type (Table 2). This result is in agreement with CZTS X-Ray diffractogram JCPDS 26-0575 database and the X-Ray diffractogram measured from the CZTS, CZT 0.5 G 0.5 S and CZTGS single crystals powder samples (see Figure 2(a)).…”

Point defects, compositional fluctuations, and secondary phases in non-stoichiometric kesterites

“…The Gaussian shaped Raman peaks indicate a certain random distribution of the bond length with a preferential value correlated to the position of the maximum intensity of the Raman peak. Typically Gaussian-like shaped Raman peaks are common in nanometric materials [58][59][60]. The phonon confinement model proposed by Nemanich et al [61] was applied by Dimitrievska et al [57] to the thin films of CZTS with different annealing times, resulting in an estimation of the phonon correlation lengths.…”

Optical phonons in the kesterite Cu2ZnGeS4semiconductor: polarized Raman spectroscopy and first-principle calculations

“…9 It has been known since the early 1970's that the Cu 2 ZnGeS 4 (CZGS) semiconductor crystallizes in either the orthorhombic or tetragonal lattice. [10][11][12] The majority of early publications on CZGS were focused on the analysis of the basic structure and electrical properties. Recently, some optical properties of the orthorhombic 13,14 and tetragonal 10,12,[15][16][17][18][19] CZGS modications have been reported.…”