Abstract: MATH/CHEM/COMP 2002, Dubrovnik, June 24-29, 2002
DEEP LEVEL NATIVE DEFECT IN InSe
Bozidar Etlinger and Mladen Pavlovic
Ruđer Bošković Institute, POB 180, HR-10002 Zagreb, Croatia
Indium selenide (InSe) is a layered semiconductor formed by graphite-like layer in which the bond between atoms is essentially covalent. Polycrystals of InSe in quartz ampoules at 850 oC are obtained through direct synthesis of stehiometric quantities of In and Se and then slowly cooled at rate 20oC/hour. Obtained samples are of n-type. InSe has an anisotropy in electric conductivity dependent on whether carrier transport is parallel or perpendicular to the layer1. The native shallow donor Ed with energy of 0.018 eV behind conduction band was found earlier2. Many authors observe the effect of partial self-compensation3,4 in InSe, which is doped by acceptor impurities (Cu, Zn, Cd). Such samples are p-type but electric conductivity is not as high as expected for applied concentration of dopands. It is also observed that Hall voltage has abnormal behaviour at the temperature below 215 oC and changes the p-type to n-type conductivity. Presumption was that such behaviour requires existence of deep-level defect situated below the half of gap (1/2Eg) and the concentration of that defect being higher than the concentration of acceptor. (Similar is observed at p-type Is doped with Fe)5. Although in non-doped InSe interstitial In gives shallow-donor, we presumed the model of deep-level native donor gives an interlayer planar complex defect which has significant influence on electric conductivity of InSe. In an attempt to find the position of such complex defect in energy gap, samples are prepared by “cleaning” ingot with zone melting process. The quartz ampoule, 13 cm long is “cleansed” 12 times with 1 cm melting band at velocity of 10 cm/h. Ingot is then separated in 23 samples from top to the bottom respectively. Termostimulated current (TSC) of every sample is measured in the temperature interval from 80 to 400 K. Measuring method used was implemented before for GaAs6. Results show one TSC peak. We calculated the energy of deep level defect at ET = (0.65 +- 0.02) eV. This value coincides with DLTS measurements for non-doped InSe (ET = 0.64 eV) 2. Considering that energy gap for InSe Eg = 1.2 eV, the value of observed deep-level native defects satisfied the preposition that the complex defect is situated below the half energy gap and that explained the anomaly behavior in p-type InSe. Configuration model shows that deep-level native defect is situated between layers.
1 B. Mari et al., Phys. stat. sol. (b) 130 (1985) 793.
2 A. Segura et al., Appl. Phys. A 31 (1983) 139.
3 S. Shigetomi et al., Jpn. J. Appl. Phys. 21 (1982) L343.
4 A. Segura et al., Appl. Phys. A 44 (1987) 249.
5 K. Wünstel et al., Appl. Phys. A 27 (1982) 207.
6 M. Pavlović et al., J. Phys. D: Appl. Phys. 28 (1995) 934.