氧化锌基材料紫外发光性质研究
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摘要
ZnO是一种宽带隙的半导体材料，室温下它的能隙宽度为3.37 eV，激子束缚能高达60 meV。自从日本和香港的科学家在1997年首次实现了室温光泵浦条件下ZnO薄膜的紫外受激发射以来，ZnO材料的研究已经成为国际光电子领域前沿课题中的研究热点。
为了探索波长更短的发光材料，我们采用溶胶凝胶方法制备出了Mg2+离子掺杂的MgxZn1-xO合金薄膜，并系统地研究了它的结构和光学性质。研究表明当x的取值小于等于0.36时，合金薄膜会保持ZnO六角形纤锌矿结构，此时薄膜的能隙宽度可以在3.4 eV到3.93 eV之间调节。从X射线衍射的结果中还可以看到，x = 0.36的合金薄膜是一种亚稳态，当热处理温度在800 ℃以下时它是纤锌矿结构，而在800 ℃以上时就出现了分相。相对来说Mg2+离子浓度较低的薄膜热稳定性较高，在1000 ℃的高温下也没有出现分相。
在室温，以He-Cd激光器325 nm线为激发源测量了合金薄膜的发光光谱，所有样品的发光光谱上都只有一个位于紫外区的发射峰，并且随着Mg2+离子的掺入MgxZn1-xO合金薄膜的发光峰向短波方向移动。其发光峰的强度随激发强度的增加而线性增大。通过分析合金薄膜样品变温条件下的发光光谱，我们得到了Mg0.05Zn0.95O合金薄膜的激子束缚能为57 meV，这一数值同ZnO的相当，所以MgZnO薄膜的紫外发光也来源于自由激子的辐射复合。
我们还通过简单的热氧化锌粒的方法制备出了ZnO微柱，微柱的平均直径为2-5 μm，长约30 μm。室温光致发光的结果表明，在较低的激发强度下除了自由激子的发光外，还能观察到来源于激子激子相互碰撞产生的P带发光，它的发光强度是激发强度二次方的函数。在单根ZnO微柱（直径有25μm）的P带发光峰上还可以观察到明显的F-P腔模式分布，通过计算得到其腔长为21μm，同微米柱的尺寸相当。进一步分析表明ZnO晶体的侧面可以作为反射镜构成谐振腔。通过测量ZnO微米柱在不同温度下的发光光谱，发现激子-激子相互碰撞产生的热激活过程，并讨论了激子激子相互作用的机理。
Dongxu Zhao (Condensed Matter Physics)
Directed by Prof. Dezhen Shen and Prof. Yichun Liu
Zinc Oxide (ZnO) is a wide band-gap semiconductor (3.37 eV at room temperature) with the high exciton binding energy of 60 meV. Since the ultraviolet (UV) lasing from ZnO was realized in 1997, the study on ZnO has attracted a great deal of attention because of the intense commercial interest in developing practical short-wavelength semiconductor diode lasers (SDLs) for the huge market needs.
In order to explore the ZnO-based material with a wider band gap, MgxZn1-xO alloy thin films were fabricated by the sol-gel deposition method. And the structure and optical properties were also studied. When x ≤ 0.36, the alloy thin films keep the wurtzite structure. And the band gap could be varied from 3.40 eV to 3.93 eV. The Mg0.05Zn0.95O and Mg0.15Zn0.85O alloys with wurtzite structure show high thermal stability up to 1000℃. However, when x is 0.36, phase separation will occur at 800℃. The intense ultraviolet photoluminescence (PL) from MgxZn1-xO alloy thin film was observed at room temperature. With increasing the contant of Mg2+ ion in the film, the peak position is blue-shifted to higher energy side. By examining the PL properties of the alloy under different temperatures, we can calculate the exciton binding energy in MgxZn1-xO to be 57 meV, which is quite equal to the binding energy of ZnO. This emission is indicative of the excitonic nature of the material.
The ZnO micro rods were also fabricated by a simple thermal oxidation method. The morphologies of the samples were detected by the scanning electron microscope (SEM), showing that the ZnO micro rods are about thirty microns long with a diameter of 5 (m. In the photoluminescence (PL) spectra, a new emission band due to the exciton-exciton collision process (P band) is observed under low excitation intensity at room temperature. And some fine structures origination from the cavity modes of the Fabry-Pérot etalon could also be seen clearly. By detectingthe PL spectra under low temperature, a thermal activation process could be seen. And the possible mechanism of P band formation is discussed.
为了探索波长更短的发光材料，我们采用溶胶凝胶方法制备出了Mg2+离子掺杂的MgxZn1-xO合金薄膜，并系统地研究了它的结构和光学性质。研究表明当x的取值小于等于0.36时，合金薄膜会保持ZnO六角形纤锌矿结构，此时薄膜的能隙宽度可以在3.4 eV到3.93 eV之间调节。从X射线衍射的结果中还可以看到，x = 0.36的合金薄膜是一种亚稳态，当热处理温度在800 ℃以下时它是纤锌矿结构，而在800 ℃以上时就出现了分相。相对来说Mg2+离子浓度较低的薄膜热稳定性较高，在1000 ℃的高温下也没有出现分相。
在室温，以He-Cd激光器325 nm线为激发源测量了合金薄膜的发光光谱，所有样品的发光光谱上都只有一个位于紫外区的发射峰，并且随着Mg2+离子的掺入MgxZn1-xO合金薄膜的发光峰向短波方向移动。其发光峰的强度随激发强度的增加而线性增大。通过分析合金薄膜样品变温条件下的发光光谱，我们得到了Mg0.05Zn0.95O合金薄膜的激子束缚能为57 meV，这一数值同ZnO的相当，所以MgZnO薄膜的紫外发光也来源于自由激子的辐射复合。
我们还通过简单的热氧化锌粒的方法制备出了ZnO微柱，微柱的平均直径为2-5 μm，长约30 μm。室温光致发光的结果表明，在较低的激发强度下除了自由激子的发光外，还能观察到来源于激子激子相互碰撞产生的P带发光，它的发光强度是激发强度二次方的函数。在单根ZnO微柱（直径有25μm）的P带发光峰上还可以观察到明显的F-P腔模式分布，通过计算得到其腔长为21μm，同微米柱的尺寸相当。进一步分析表明ZnO晶体的侧面可以作为反射镜构成谐振腔。通过测量ZnO微米柱在不同温度下的发光光谱，发现激子-激子相互碰撞产生的热激活过程，并讨论了激子激子相互作用的机理。
Dongxu Zhao (Condensed Matter Physics)
Directed by Prof. Dezhen Shen and Prof. Yichun Liu
Zinc Oxide (ZnO) is a wide band-gap semiconductor (3.37 eV at room temperature) with the high exciton binding energy of 60 meV. Since the ultraviolet (UV) lasing from ZnO was realized in 1997, the study on ZnO has attracted a great deal of attention because of the intense commercial interest in developing practical short-wavelength semiconductor diode lasers (SDLs) for the huge market needs.
In order to explore the ZnO-based material with a wider band gap, MgxZn1-xO alloy thin films were fabricated by the sol-gel deposition method. And the structure and optical properties were also studied. When x ≤ 0.36, the alloy thin films keep the wurtzite structure. And the band gap could be varied from 3.40 eV to 3.93 eV. The Mg0.05Zn0.95O and Mg0.15Zn0.85O alloys with wurtzite structure show high thermal stability up to 1000℃. However, when x is 0.36, phase separation will occur at 800℃. The intense ultraviolet photoluminescence (PL) from MgxZn1-xO alloy thin film was observed at room temperature. With increasing the contant of Mg2+ ion in the film, the peak position is blue-shifted to higher energy side. By examining the PL properties of the alloy under different temperatures, we can calculate the exciton binding energy in MgxZn1-xO to be 57 meV, which is quite equal to the binding energy of ZnO. This emission is indicative of the excitonic nature of the material.
The ZnO micro rods were also fabricated by a simple thermal oxidation method. The morphologies of the samples were detected by the scanning electron microscope (SEM), showing that the ZnO micro rods are about thirty microns long with a diameter of 5 (m. In the photoluminescence (PL) spectra, a new emission band due to the exciton-exciton collision process (P band) is observed under low excitation intensity at room temperature. And some fine structures origination from the cavity modes of the Fabry-Pérot etalon could also be seen clearly. By detecting
引文
1. 王新强 杜国同 姜秀英 王金忠 杨树人. ZnO薄膜的研究进展.
半导体光电，2000 (4): 233-237
2. 柯炼 缪熙月 魏彦峰 王杰 王迅. II-VI族半导体激光器的新材料-ZnO量
子点. 物理, 1999 (1): 30-34
3. 王卿璞 张德恒 于永芹 黄柏标. ZnO薄膜材料的发光特性. 半导体情报.
2001(4): 48-53
4. J. M. Hvam, Exciton-exciton interaction and laser emission in High-purity ZnO,
Solid State Communications, 1973(12):95-97
5. Z.K.Tang, G.K.L.Wong, P.Yu, et al., Room-temperature ultraviolet laser emission from self-assembled ZnO microcrystallite thin films, Appl.Phys.Lett., 1998, 72(27): 3270-3272
6. D. M. Bagnall, Y. F. Chen, Z. Zhu, et al., Opticallly pumped lasing of ZnO at room temperature., Appl.PhysLett., 1997, 70(17): 2230
7. H. Cao, Y. G. Zhao, H. C. Ong, et al., Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films., Appl.Phys.Lett., 1998, 73(25): 3656
8. P. Yu, Z. K. Tang, G. K. L. Wong, et al., Ultraviolet spontaneous and stimulated emission from ZnO mictrocrystallite thin films at room temperature., Solid State Com., 1997, 103(8): 459
9. P. Yu, Z. K. Tang, G. K. L. Wong, et al., Room-temperature gain spectra and lasing in micro crystalline ZnO thin film., J. Crystal Growth., 1998, 184/185: 601
10. D. M. Bagnall, Y. F. Chen, Z. Zhu, et al., High temperature excitonic stimulated emission from ZnO epitaxial layers., Appl.Phys.Lett., 1998, 73(8): 1038
11. Laser light from a handful of dust., Science., 1999, 284: 24-25
12. Will UV Lasers Beat the Blues?, Science., 1997, 276: 895
半导体光电，2000 (4): 233-237
2. 柯炼 缪熙月 魏彦峰 王杰 王迅. II-VI族半导体激光器的新材料-ZnO量
子点. 物理, 1999 (1): 30-34
3. 王卿璞 张德恒 于永芹 黄柏标. ZnO薄膜材料的发光特性. 半导体情报.
2001(4): 48-53
4. J. M. Hvam, Exciton-exciton interaction and laser emission in High-purity ZnO,
Solid State Communications, 1973(12):95-97
5. Z.K.Tang, G.K.L.Wong, P.Yu, et al., Room-temperature ultraviolet laser emission from self-assembled ZnO microcrystallite thin films, Appl.Phys.Lett., 1998, 72(27): 3270-3272
6. D. M. Bagnall, Y. F. Chen, Z. Zhu, et al., Opticallly pumped lasing of ZnO at room temperature., Appl.PhysLett., 1997, 70(17): 2230
7. H. Cao, Y. G. Zhao, H. C. Ong, et al., Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films., Appl.Phys.Lett., 1998, 73(25): 3656
8. P. Yu, Z. K. Tang, G. K. L. Wong, et al., Ultraviolet spontaneous and stimulated emission from ZnO mictrocrystallite thin films at room temperature., Solid State Com., 1997, 103(8): 459
9. P. Yu, Z. K. Tang, G. K. L. Wong, et al., Room-temperature gain spectra and lasing in micro crystalline ZnO thin film., J. Crystal Growth., 1998, 184/185: 601
10. D. M. Bagnall, Y. F. Chen, Z. Zhu, et al., High temperature excitonic stimulated emission from ZnO epitaxial layers., Appl.Phys.Lett., 1998, 73(8): 1038
11. Laser light from a handful of dust., Science., 1999, 284: 24-25
12. Will UV Lasers Beat the Blues?, Science., 1997, 276: 895