Mr. Mim Lal Nakarmi Profile

Mim Lal Nakarmi

Chair, Dept. of Physics at Brooklyn College

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Publications (5)

Proceedings Article | 15 February 2006 Paper

Time-resolved photoluminescence studies of Mg-doped AlN epilayers

N. Nepal, M. Nakarmi, J. Y. Lin, H. X. Jiang

Proceedings Volume 6118, 61180E (2006) https://doi.org/10.1117/12.651856

KEYWORDS: Aluminum nitride, Magnesium, Excitons, Picosecond phenomena, Gallium nitride, Aluminum, Gallium, Electromagnetic coupling, Luminescence, Metalorganic chemical vapor deposition

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Proceedings Article | 20 October 2004 Paper

Mg-doped Al-rich AlGaN alloys for deep UV emitters

Mim Nakarmi, Kyoung Hoon Kim, Kai Zhu, Jing Yu Lin, Hong Xing Jiang

Proceedings Volume 5530, (2004) https://doi.org/10.1117/12.566192

KEYWORDS: Magnesium, Light emitting diodes, Aluminum, Gallium, Deep ultraviolet, Temperature metrology, Aluminum nitride, Doping, Crystal optics, Metalorganic chemical vapor deposition

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Proceedings Article | 16 June 2004 Paper

Time-resolved photoluminescence studies of Si- and Mg-doped AlN epilayers

K. Nam, M. Nakarmi, J. Li, Jing Yu Lin, Hongxing Jiang

Proceedings Volume 5352, (2004) https://doi.org/10.1117/12.525752

KEYWORDS: Aluminum nitride, Silicon, Magnesium, Doping, Aluminum, Electromagnetic coupling, Picosecond phenomena, Excitons, Gallium nitride, Gallium

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Si and Mg-doped AlN epilayers were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates. Deep ultraviolet (UV) picosecond time-resolved photoluminescence (PL) spectroscopy has been employed to study the optical transitions in the grown epilayers. The donor bound exciton (or I₂) transition was found to be the dominant recombination line in Si-doped AlN epilayers at 10 K and its emission intensity decreases with increasing Si dopant concentration. Doping induced band-gap renormalization effect has also been observed. Time-resolved PL results on Si-doped AlN revealed a linear decrease of PL decay lifetime with increasing Si dopant concentration, which was believed to be a direct consequence of the doping enhanced nonradiative recombination rates and corroborated the PL intensity results. For Mg-doped AlN epilayers, two emission lines at 4.70 and 5.54 eV have been observed at 10 K, which were assigned to donor-acceptor pair transitions involving Mg acceptor and two different donors (one deep and one shallow). From PL emission spectra and the temperature dependence of the PL emission intensity, a binding energy of 0.51 eV for Mg acceptor in AlN was determined. Together with previous experimental results, the Mg acceptor activation energy in AlGaN as a function of the Al content for the entire AlN composition range was obtained. The average hole effective mass in AlN was also deduced to be about 2.7 m₀ from the experimental value of Mg binding energy together with the effective mass theory. Although Mg acceptors are an effective mass state in ultra-large bandgap AlN, as a consequence of this large acceptor binding energy of 0.51 eV, only a very small fraction (about 10^-9) of Mg dopants can be activated at room temperature in Mg-doped AlN. Decay lifetimes of these emission lines are also measured as functions of emission energy, temperature, and excitation intensity. The implications of our finding on the applications of AlN epilayers for many novel devices will also be discussed.

Proceedings Article | 30 May 2003 Paper

Epitaxial growth and time-resolved photoluminescence studies of AIN epilayers

Ki-Bum Nam, Jing Li, M. Nakarmi, Jing Lin, Hongxing Jiang

Proceedings Volume 4992, (2003) https://doi.org/10.1117/12.479274

KEYWORDS: Excitons, Gallium nitride, Picosecond phenomena, Semiconductors, Temperature metrology, Metalorganic chemical vapor deposition, Aluminum nitride, Luminescence, Deep ultraviolet, Sapphire

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Proceedings Article | 11 June 2002 Paper

Time-resolved photoluminescence studies of Al-rich AlGaN alloys

Jing Li, Ki-Bum Nam, Tom Oder, KyoungHoon Kim, M. Nakarmi, Jing Lin, Hongxing Jiang

Proceedings Volume 4643, (2002) https://doi.org/10.1117/12.470429

KEYWORDS: Aluminum, Doping, Silicon, Magnesium, Gallium, Luminescence, Temperature metrology, Gallium nitride, Excitons, Metalorganic chemical vapor deposition

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Si-doped n-type Al_xGa_1MINxN alloys with x up to 0.5 and Mg-doped p-type Al_xGa_1-xN alloys with x up to 0.27 were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire substrates. For the n-type Al_xGa_1-xN, we achieved highly conductive alloys for x up to 0.5. An electron concentration as high as 1x10¹⁸cm^-3 was obtained in Si-doped Al_0.5Ga_0.5N alloys with an electron mobility of 16 cm$_2)Vs at room temperature, as confirmed by Hall-effect measurements. Our results also revealed that the conductivity of Al_xGa_1-xN alloys continuously increases with an increase of Si doping level for a fixed value of Al content (X<0.5), the conductivities of Al_xGa_1-xN alloys decrease with increasing Al content for a given doping level; the critical Si-doping concentration needed to convert insulating Al_xGa$1-x)N with high Al contents (X>=0.4) to n- type conductivity is about 1 x 10¹⁸cm^-3. Time- resolved photoluminescence studies carried out on these materials have shown that Si-doping reduces the effect of carrier localization in Al_xGa_1-xN alloys and a sharp drop in carrier localization energy occurs when the Si doping concentration increases above 1x10¹⁸cm^-3, which directly correlates with the observed electrical properties. For the Mg-doped Al_xGa_1-xN alloys, p-type conduction was achieved for x up to 0.27, as confirmed by variable temperature Hall measurements. Emission lines of band-to-impurity transitions of free electrons with neutral Mg acceptors as well as localized excitons have been observed in the p-type Al_xGa_1-xN alloys. The Mg acceptor activation energies E_A were deduces from photoluminescence spectra and were found to increase with Al content and agreed very well with those obtained by Hall measurements. From the measured activation energy as a function of Al content, E_A versus x, the resistivity of Mg-doped Al_xGa_1-x with high Al contents can be deduced. Our results have also shown that PL measurements provide direct means of obtaining E_A especially where this cannot be obtained accurately by electrical methods due to high resistance of p-type Al_xGa_1-xN with high Al content.

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