Abstract and additional information:
Metalorganic vapor epitaxy (MOVPE) is an important potential technique for the realization of ZnO based devices. ZnO nanowires (NWs) are a promising avenue of investigation due to their high quality optical and structural properties when compared with planar films. Control of dopant impurities, both n- and p-type, is very critical for the NWs based devices. Group-III elements (Al, Ga and In) are well known shallow donors in ZnO.1 Among group IV elements; carbon is a very common unintentional impurity during ZnO growth, especially for the MOVPE technique at low growth temperatures. Possible p-type dopants for ZnO are group-V impurities such as N, P, As and Sb.1 Dopant concentration can be precisely controlled over a wide range using organometallic sources in MOVPE technique. In this talk, I will be presenting our recent demonstrations of controlled doping of Al, In, C and Sb impurities in ZnO NWs by means of low temperature optical spectroscopy technique.2-4
Extremely sharp low temperature photoluminescence (PL) linewidths, as low as 0.17 meV, are observed in nominally undoped ZnO nanowires grown by MOVPE.2 These are among the narrowest lines reported for ZnO PL, even for bulk growth, despite growth on highly mismatched sapphire substrates. MOVPE allows the control of group III dopants over a wide range of doping levels. The addition of indium and aluminum dopants resulted in the appearance of their corresponding neutral (D0X) and ionized (D+X) donor bound exciton transitions with linewidths comparable to those of nominally undoped material.2 Antimony doped ZnO nanowires exhibited shallow D0X transition at 3364.3 meV, which is the shallowest among the neutral donor bound exciton transitions so far observed in ZnO.3 The low formation energy indicated by our annealing measurements indicates that the responsible donor is a complex, possibly SbZn-VZn. Carbon doped ZnO NWs exhibited several shallow donor bound exciton PL transitions in the range of 3360.8 to 3361.9 meV, which are close to previously reported emission lines due to excitons bound to donor point defects such as Ga, Al, In and H.4 The observation of two electron satellites for these carbon related emission lines enabled the determination of the donor binding energies. The dependence of exciton localization energy on donor binding energy departs somewhat from the usual linear relationship observed for group III donors indicating a qualitatively different central cell potential, as one would expect for a complex. All these results will be presented and discussed.
1. B. K. Meyer et al., Phys. Status Solidi B 241, 231 (2004).
2. E. Senthil Kumar et al., Semicond. Sci. Technol. 28, 045014 (2013).
3. E. Senthil Kumar et al., Appl. Phys. Lett. 102, 132105 (2013).
4. F. Mohammadbeigi, E. Senthil Kumar et al., J. Appl. Phys. (accepted)
This Seminar will be chaired by Anton Plech.
A lunch with the speaker in our Casino at 12:15 is scheduled. Please notify Anton Plech in advance, if you wish to participate in the lunch.
Please specify, when you wish a vegetarian meal. The KIT-guideline restricts the number of internal participants.