1. Phw. Chm. Solids Vol. Rimed in Cm1 Britain.
1. pp. 91-92.
s3.m+ 0.00 PtrpMonhpk
NOTE OF Cd-DOPED
S. SHIGETOMI,~ H. OHKUBO~and T. IKARI$ tDepartment of Physics, Kurume University, 1635 Mii-machi, Kurume, Fukuoka 830, Japan SDepartment of Electronic Engineering, Miyazaki University, 1-I Gakuen-kibanadai, Miyazaki 889-2 1, Japan (Received
1I April 1988; accepted in revisedform 9 August 1989)
Abstract-Photoluminescence (PL) spectra of Cd-doped InSe were measured in the 77 to 170 K temperature range. A new emission band at I.21 eV is observed upon doping with Cd atoms and its PL intensity increases with increasing dopant concentration. We find, from the activation energy for the temperature dependence of PL intensity, that the I.21 eV emission is not due to the band-impurity transition. Keywords: Cd-doped I&e. impurity level, photoluminescence,
sum of the I .2 I eV emission energy and the 0. I7 eV thermal quenching activation energy is larger than the value of the band gap. Thus the transition of the 1.21 eV band cannot be explained by the band-impurity recombination. The origin of the recombination mechanism of I.21 eV emission is not clear at present; further studies and analysis are required. In conclusion. it was demonstrated for the first time experimentally that the new emission band is formed at I .21 eV in the PL spectra of Cd-doped InSe and that it is not
In recent years, impurity levels in the layered III-VI compound InSe have been investigated by doping with elements of the II, IV, and VII groups. Deep level transient spectroscopy and Hall effect measurements on Cl- and Sri-doped n-InSe have been carried out by Segura et al. [ 1). They found the impurity levels attributed to Cl (0.31 eV) and Sn atoms (0.044 and 0.12 ev). We reported the photoluminescence spectra of &-doped p-InSe. and have shown that the 1.17 eV band associated with the Zn acceptor-vacancy center can be explained by self-activated luminescence in terms of a configuration coordinate model . The acceptor ionization energy of 0.45 eV was also observed in Cd-doped p-I& by using Hall measurements . In this note, photoluminescence (PL) spectra in Cd-doped p-InSe are reported. Single crystals of Cd-doped I& were grown by the conventional Bridgman technique. Doping by Cd was in the range from stoichiometric InSe to 0.1-5 at.%. The Cd-doped samples were p-type. The hole concentrations of 0.1.1. and 5 at.% Cd-doped samples were I x 10”. 4 x IO”, and 2 x lO”cm- at room temperature, respectively. The samples were prepared by cleaving an ingot parallel to the layer which was perpendicular to the c-axis with typical sample dimensions of I2 x 3 x 0.3 mm’. The PL measurements were carried out in the 77-170 K temperature region using an Ar ion laser (514.5 nm) as an excitation source. The emission spectra were detected with a PbS photoresistor employing the lock-in technique. Figure 1 shows the PL spectra of undoped and Cd-doped InSe at 77 K. For both the undoped and Cd-doped samples, the emission band at 1.33 eV was observed and assigned to the transition due to free exciton annihilation [4,5]. A new broad emission band at I.21 eV appears in the PL spectra of all Cddoped samples and the ratio of its intensity to the 1.33 eV free exciton band increases with increasing dopant concentration. The high energy side of the emission band can be described by a Gaussian curve while the low energy side of the band shows a non-Gaussian shape. The thermal quenching behavior of the 1.21 eV band is shown in Fig. 2. A semilog plot of the PL intensity as a function of the reciprocal temperature gives a straight line at temperatures above 120 K. The activation energy derived from the slope of the straight line is 0.17 eV. The band gap of InSe is 1.34eV at 77 K . If we assume that the transitions occur from the conduction band to the impurity level and/or the impurity level to the valence band, then the
Fig. 1. PL spectra of undoped and Cd-doped InSe at 77 K: (1) undoped: (2) 0.1%; (3) I %; and (4) 5% Cd-doped. 91
Technical Note due to the transition between the band and the impurity level. Acknowledgemenu-We wish to thank Profs Yutaka Koga and Shigenobu Shigetomi of Kurume University for helpful discussions.
Fig. 2. Variation of the PL intensity of the 1.21 eV band with the reciprocal temperature.
Segura A., Wiinstel K. and Chevy A., Appl. Phys. A31, 139 (1983). Ikari T., Shigetomi S., Koga Y. and Shigetomi S., Phys. Sfafw Solidi (b) 103, K81 (1981). Shigetomi S., Ikari T., Koga Y. and Shigetomi S., Phys. Starus Solidi (a) 108, KS3 (1988). Bakumenko V. L.. Kovalyuk Z. D., Kurbatov L. N. and Chishko V. F., Soviet Phys. Semicond. 10, 740 (1976). 5. Ikari T. and Shigetomi S., Phys. Srofus Solidi (b) 124, K49 (1984). 6. Camassel J., Merle P., Mathieu H. and Chevy A., Phys. Rev. B12, 4718 (1978).