Luminescence and ESR Spectra of GaN:Si below and above Mott Transition
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Internet Journal Nitride Semiconductor Research
Luminescence and ESR Spectra of GaN:Si below and above Mott Transition K. Paku‚a1, M. Wojdak1, M. Palczewska2, B. Suchanek2 and Jacek M. Baranowski 2 1Institute 2Institute
of Experimental Physics, Warsaw University, of Electronic Materials Technology,
(Received Monday, June 22, 1998; accepted Wednesday, October 7, 1998)
Investigations of luminescence and ESR of silicon doped GaN layers are presented. The room temperature electron concentration in the investigated layers ranged from 1.7x1017 cm-3 to 7x1018 cm-3. The layer with the highest electron concentration has metallic conductivity. The ESR investigation revealed the presence of a characteristic asymmetric resonance whose intensity grows with increasing silicon impurity concentration. This resonance, corresponding to perpendicular g=1.985 and parallel g=1.983 has been observed in Si doped layers with electron concentration below the Mott transition. It seems that the ESR resonance is due to isolated Si donors. It has been found that the total PL emission increases with the silicon concentration, and is strongest in the layer with metallic conductivity. This indicates that silicon impurities eliminate non-radiative recombination centers or they create a new path of radiative recombination. The AFM and low temperature PL measurements indicate that strain relief via creation of pinholes may be responsible for the increase of radiative emission in GaN:Si epilayers.
1
Introduction.
The group III nitride technology has reached such a high level that the first blue cw laser operating at room temperature has been demonstrated [1]. For blue and UV emitters, the understanding of radiative and non-radiative recombination paths is of crucial importance. Electrical, ESR and PL measurements have been performed to understand the efficient radiative recombination channel in GaN:Si. 2
Experimental
GaN:Si was grown by the atmospheric pressure MOCVD technique, starting from TMG, NH3 and SiH4, and using (0001) sapphire substrates. The GaN buffer layer was grown at 560°C, followed by a Si doped epitaxial layer grown at 1060°C. All the layers have been grown under the same growth conditions, except for the monosilane flow rate, in order to get GaN:Si layers with net electron concentrations of 1.7x1017 – 7x1018 cm-3. The thickness of all the epilayers was approximately 3.5µm. The thickness of the buffer layer, which is of critical importance, was chosen in such way that smooth layers with mirror-like surfaces without hexagonal hillocks were grown.
The Hall effect, electron spin resonance (ESR), atomic force microscope (AFM) and photoluminescence (PL) techniques were applied to characterize the physical properties of the GaN:Si layers. The electron concentration was determined using the van der Pauw configuration and PL was performed using the 325nm line of a He-Cd 10mW laser. 3
Experimental results and discussion.
Results of electrical measurements of four GaN:Si layers grown with various silicon concentrations are shown in
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