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* XTEM images show no threading dislocations (TDs) in the GaN nanowires, even though TDs were observed in the planar GaN film beneath the growth mask. This was found to be the case for GaN nanowire growth on all substrates, including growth on silicon (111). | * XTEM images show no threading dislocations (TDs) in the GaN nanowires, even though TDs were observed in the planar GaN film beneath the growth mask. This was found to be the case for GaN nanowire growth on all substrates, including growth on silicon (111). | ||
* recorded band-edge PL peak intensity for the nanowire sample was 100 times greater than that measured for a 5 micron planar GaN film and more than 200 times greater than that measured for a 0.6 micron planar GaN film. Much of this intensity increase is undoubtedly due to the geometry of a nonplanar nanowire sample, where the input coupling of the PL pump beam and the out-coupling of the resulting PL will both be increased significantly. | * recorded band-edge PL peak intensity for the nanowire sample was 100 times greater than that measured for a 5 micron planar GaN film and more than 200 times greater than that measured for a 0.6 micron planar GaN film. Much of this intensity increase is undoubtedly due to the geometry of a nonplanar nanowire sample, where the input coupling of the PL pump beam and the out-coupling of the resulting PL will both be increased significantly. | ||
====[http://www.sciencedirect.com/science/article/pii/S0169433209002359 InGaN nanorod arrays grown by molecular beam epitaxy: Growth mechanism structural and optical properties<ref name="Wu">Wu, K.M., Pan, Y. & Liu, C., 2009. InGaN nanorod arrays grown by molecular beam epitaxy: Growth mechanism structural and optical properties. Applied Surface Science, 255(13-14), pp.6705-6709</ref>]==== | |||
'''Abstract:''' Vertically c-axis-aligned InGaN nanorod arrays were synthesized on c-plane sapphire substrates by radio-frequency molecular beam epitaxy. In situ reflection high-energy electron diffraction was used to monitor the growth process. X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscope, and photoluminescence were used to investigate the structural and optical properties of the nanorods. The growth mechanism was studied and a growth model was proposed based on the experimental data. A red shift of photoluminescence spectrum of InGaN nanorods with increasing growth time was found and attributed to the partial release of stress in the InGaN nanorods. | |||
* Initially RHEED pattern was streaky, indicating a two-dimensional (2D) growth with a smooth surface at the initial stage. As growth proceeded, one observed mixed RHEED pattern including spots and lines, but the lines were still streaky. After deposition for 13 min, circular spotty RHEED pattern was observed; indicating a three-dimensional (3D) island growth, circular spotty RHEED pattern lasted for 30 min. | |||
* Afterwards the circular spotty RHEED pattern broadens along the direction parallel to the surface; this is typically the RHEED pattern of nanorods. Such a pattern suggested that the nanorods nucleated on the rough InGaN layer, grew up while narrowed, nanorods were single crystalline and collectively grew along the c-axis. | |||
* misfit accommodation can take place through the onset of islanding and generating surface roughness in strained epitaxial systems. | |||
* growth-mode transition from layer-by-layer (2D) growth to 3D islanding occurs quite abruptly when a certain critical strain was reached. In mismatched InGaN-sapphire system, according to RHEED observations, strained InGaN layer started growing nearly pseudomorphical to sapphire and presented relatively smooth surface, when layer thickness exceeded a certain critical layer thickness (CLT) of about 30 nm, strained InGaN layer started to relax and 3D islands began to form. | |||
* For layer thicknesses well above CLT, the surface became very rough and was dominated by large 3D islands. | |||
* formation of InGaN nanorod array can be roughly divided into following stages: Firstly, InGaN thin film grew pseudomorphically on c-plane sapphire, and then 3D islands formed when layer exceeded the CLT. InGaN nanorods started to nucleate on rough InGaN layer and then grew up. At last, the InGaN nanorods coalescenced. | |||
* increased crystal growth times improves crystal quality. | |||
* band gap of strained InGaN films is larger than that of the relaxed due to the compressive stresses | |||
* Such a stress in InGaN nanorods could not be eliminated until length exceeded several micrometers | |||
== References == | == References == | ||
<references/> | <references/> | ||
Revision as of 07:10, 12 December 2011
| This is in a series of literature reviews on InGaN solar cells, which supported the comprehensive review by D.V.P. McLaughlin & J.M. Pearce, "Progress in Indium Gallium Nitride Materials for Solar Photovoltaic Energy Conversion"Metallurgical and Materials Transactions A 44(4) pp. 1947-1954 (2013). open access Others: InGaN solar cells| InGaN PV| InGaN materials| InGan LEDs| Nanocolumns and nanowires| Optical modeling of thin film microstructure| Misc. |
This page describes selected literature available on InGaN based LED and LASER devices.
The Controlled Growth of GaN Nanowires[1]
Abstract: This paper reports a scalable process for the growth of high-quality GaN nanowires and uniform nanowire arrays in which the position and diameter of each nanowire is precisely controlled. The approach is based on conventional metalorganic chemical vapor deposition using regular precursors and requires no additional metal catalyst. The location, orientation, and diameter of each GaN nanowire are controlled using a thin, selective growth mask that is patterned by interferometric lithography. It was found that use of a pulsed MOCVD process allowed the nanowire diameter to remain constant after the nanowires had emerged from the selective growth mask. Vertical GaN nanowire growth rates in excess of 2 μm/h were measured, while remarkably the diameter of each nanowire remained constant over the entire (micrometer) length of the nanowires. The paper reports transmission electron microscopy and photoluminescence data.
- Reports a scalable process for the growth of high-quality GaN nanowires and uniform nanowire arrays in which the position and diameter of each nanowire is precisely controlled based on conventional metal-organic chemical vapor deposition (MOCVD) using trimethygallium (TMGa) and ammonia (NH3) and requires no additional metal catalyst.
- The location, orientation, and diameter of each GaN nanowire are controlled using a thin, selective-growth mask that is patterned by interferometric lithography.
- This method enables to fabricate high quality symmetrical hexagonal sidewall facets over the entire micrometer length of nanowires.
- This method was carried out in two phases, first phase used continous MOCVD till nanowires emerged out of mask and second phase was pulse MOCVD to fabricate nanowires emerged out of mask at the end of phase one, using pulsed MOCVD in second phase maintained the quality of nanowires and were highly alligned and ordered as desired with respect to the mask.
- diameter of the nanowire remains constant as it emerges from the growth mask, confirming from XTEM images that the nanowire diameter is indeed controlled by the diameter of the growth mask aperture.
- XTEM images show no threading dislocations (TDs) in the GaN nanowires, even though TDs were observed in the planar GaN film beneath the growth mask. This was found to be the case for GaN nanowire growth on all substrates, including growth on silicon (111).
- recorded band-edge PL peak intensity for the nanowire sample was 100 times greater than that measured for a 5 micron planar GaN film and more than 200 times greater than that measured for a 0.6 micron planar GaN film. Much of this intensity increase is undoubtedly due to the geometry of a nonplanar nanowire sample, where the input coupling of the PL pump beam and the out-coupling of the resulting PL will both be increased significantly.
InGaN nanorod arrays grown by molecular beam epitaxy: Growth mechanism structural and optical properties[2]
Abstract: Vertically c-axis-aligned InGaN nanorod arrays were synthesized on c-plane sapphire substrates by radio-frequency molecular beam epitaxy. In situ reflection high-energy electron diffraction was used to monitor the growth process. X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscope, and photoluminescence were used to investigate the structural and optical properties of the nanorods. The growth mechanism was studied and a growth model was proposed based on the experimental data. A red shift of photoluminescence spectrum of InGaN nanorods with increasing growth time was found and attributed to the partial release of stress in the InGaN nanorods.
- Initially RHEED pattern was streaky, indicating a two-dimensional (2D) growth with a smooth surface at the initial stage. As growth proceeded, one observed mixed RHEED pattern including spots and lines, but the lines were still streaky. After deposition for 13 min, circular spotty RHEED pattern was observed; indicating a three-dimensional (3D) island growth, circular spotty RHEED pattern lasted for 30 min.
- Afterwards the circular spotty RHEED pattern broadens along the direction parallel to the surface; this is typically the RHEED pattern of nanorods. Such a pattern suggested that the nanorods nucleated on the rough InGaN layer, grew up while narrowed, nanorods were single crystalline and collectively grew along the c-axis.
- misfit accommodation can take place through the onset of islanding and generating surface roughness in strained epitaxial systems.
- growth-mode transition from layer-by-layer (2D) growth to 3D islanding occurs quite abruptly when a certain critical strain was reached. In mismatched InGaN-sapphire system, according to RHEED observations, strained InGaN layer started growing nearly pseudomorphical to sapphire and presented relatively smooth surface, when layer thickness exceeded a certain critical layer thickness (CLT) of about 30 nm, strained InGaN layer started to relax and 3D islands began to form.
- For layer thicknesses well above CLT, the surface became very rough and was dominated by large 3D islands.
- formation of InGaN nanorod array can be roughly divided into following stages: Firstly, InGaN thin film grew pseudomorphically on c-plane sapphire, and then 3D islands formed when layer exceeded the CLT. InGaN nanorods started to nucleate on rough InGaN layer and then grew up. At last, the InGaN nanorods coalescenced.
- increased crystal growth times improves crystal quality.
- band gap of strained InGaN films is larger than that of the relaxed due to the compressive stresses
- Such a stress in InGaN nanorods could not be eliminated until length exceeded several micrometers
References
- ↑ Hersee, S.D., Sun, X. & Wang, X., 2006. The Controlled Growth of GaN Nanowires. Nano Lett., 6(8), pp.1808-1811
- ↑ Wu, K.M., Pan, Y. & Liu, C., 2009. InGaN nanorod arrays grown by molecular beam epitaxy: Growth mechanism structural and optical properties. Applied Surface Science, 255(13-14), pp.6705-6709