Dr. Zhao Yang Fan Profile

Dr. Zhao Yang Fan

at Kansas State Univ

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Proceedings Article | 6 February 2007 Paper

Achieving conductive high Al-content AlGaN alloys for deep UV photonics

Z. Fan, J. Lin, H. Jiang

Proceedings Volume 6479, 64791I (2007) https://doi.org/10.1117/12.715046

KEYWORDS: Aluminum nitride, Aluminum, Gallium, Magnesium, Zinc, Silicon, Gallium nitride, Deep ultraviolet, Excitons, Doping

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Recent progresses in epitaxial growth and fundamental studies on electrical and optical properties of high Al-content AlGaN alloys with Si, Mg, and Zn doping are presented. For Si doped Al_xGa1-_xN, the Si activation energy was determined for x = 0 up to 1, and the resistivity of n-Al_xGa1-_xN was found to increases by one order of magnitude when Al content is increased by ~ 8%. From photoluminescence (PL) studies, three groups of deep impurity transitions were observed, related with deep level acceptors involving cation vacancy and its complexes: (VIII)^3-, (VIII-complex)², and (VIII-complex)^1-, which are electron traps and compensating centers. By optimizing the growth processes to reduce the densities of cation vacancy and its complexes, the n-type conductivity of Al_xGa1-_xN was significantly improved. A record low room temperature n-type resistivity of 0.0075 Ω•cm has been obtained for Al_0.7Ga_0.3N, and n-type conduction in pure AlN has also been achieved. We also review the electrical and optical measurement results of Mgdoped AlGaN and AlN. It was found that the overall material quality and conductivity of Mg-doped AlN are strongly correlated with the PL emission intensity of the nitrogen vacancy (V_N ³⁺) related transition. Improved conductivity was obtained by suppressing the V_N³⁺ related emission line, which was attributed to the reduced hole compensation by V_N³⁺. With the identification of the emission peaks associated with V_N³⁺ hole compensating centers, the p-type conductivity of high Al-content AlGaN alloys was improved by monitoring and suppressing the intensity of the V_N³⁺ related emission lines. P-type conduction in Al_xGa1-_xN (x > 0.7) was confirmed at elevated temperatures (> 700 K). The possibility of using Zn as an alternative p-type dopant was also studied. It was found that contrary to the calculation, the energy level of Zn acceptor in AlN was about 0.74 eV, which is 0.23 eV deeper than Mg level in AlN.

Proceedings Article | 28 February 2006 Paper

III-nitride deep ultraviolet micro- and nano-photonics

Z. Fan, J. Lin, H. Jiang

Proceedings Volume 6127, 61271C (2006) https://doi.org/10.1117/12.641250

KEYWORDS: Aluminum, Gallium, Light emitting diodes, Deep ultraviolet, Magnesium, Sapphire, Aluminum nitride, Microlens array, Ultraviolet light emitting diodes, Polarization

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Recent progresses in epitaxial growth, fundamental studies of high Al content AlGaN alloys with Si and Mg doping, light polarization properties, and deep UV LEDs combined with microlens or photonic crystal structure to improve light extraction are presented. For Si doped Al_0.7Ga_0.3N, a room temperature n-type resistivity as low as 0.0075 Ω•cm has been obtained. We have also achieved n-AlN with a free electron concentration and mobility of about 1.0 x 10¹⁷cm^-3 and 2 cm²/Vs, respectively. For Mg doped Al_0.7Ga_0.3N, we have obtained a resistivity around 10⁵ Ω cm at room temperature and confirmed p-type conduction at elevated temperatures (> 700 K) with a resistivity of about 40 Ω cm at 800 K. Based on the optimized material growth, 280 nm deep UV LED with forward voltage of 6.7 V, and output power of 0.35 mW has been achieved at 20 mA. To enhance light extraction efficiency, sapphire microlens array was monolithically integrated on flip-chip bonded deep UV LED substrates; a light extraction enhancement of 55% was achieved. To improve the transverse light extraction, photonic crystal structures were incorporated into the devices, and significant light extraction enhancement was achieved.

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