研究目的
Investigating the growth mechanism and properties of self-assembled InN nanocolumns on Al covered Si(111) substrates by plasma-assisted molecular beam epitaxy.
研究成果
We grew InN NCs on Si(111) substrates with high crystalline quality at a low growth temperature of 400 ?C. Our results evidence that the Al thin layer covered Si(111) substrate avoided substrate nitridation and also promoted the formation of unintentional AlN when the N-plasma was ignited. We found that the process of InN nucleation at 400 ?C started by a layer–layer (2D) growth, followed by the growth of 3D islands, generating a transition of 2D to 3D growth. We identified nanocolumns with cylindrical and conical shapes and heights between 250 and 380 nm. The diameter of the cylindrical NCs was below 50 nm and for the conical NCs below of 150 nm. HR-TEM analysis revealed that the InN NCs were free of structural defects and strain. With Raman spectroscopy, the A1(TO), E2h, and A1(LO) phonon modes corresponding to the InN are visible. At a temperature of 20 K, the PL measurement showed an infrared emission at 0.72 eV with a FWHM of 37 meV. The PR characterization was also employed to obtain the energy transition of the NCs. The transition was found at 0.712 eV at the temperature of 300 K. These results are useful for the development of devices with improved performance as well as to obtain compatibility of the nitrides with current microelectronic industry based on silicon.
研究不足
The use of low substrate temperatures is very important to avoid In interdiffusion and In droplet formation. The growth of InN NCs at a growth temperature of 400 ?C by rf-plasma-assisted Molecular Beam Epitaxy (RF-MBE) was studied, but higher temperatures might offer different properties.
1：Experimental Design and Method Selection:
The growths were carried out in a Riber C21 MBE system equipped with a radio frequency (RF) nitrogen plasma source, and standard Knudsen cells. The growth stages were monitored in-situ by RHEED, with an acceleration voltage of 12 kV.
2：Sample Selection and Data Sources:
Si(111) substrate was chemically treated to remove the native silicon oxides and to form a thin fresh layer of oxides. Then, the substrate was loaded into the growth chamber, where it was thermally cleaned at 900 ?C for 10 min.
3：List of Experimental Equipment and Materials:
Riber C21 MBE system, RF nitrogen plasma source, Knudsen cells, JEOL JSM-7401F SEM, Jeol JEM 2010 HR-TEM, MRD Xpert system from Panalytical for HR-XRD, NT-MDT Integra Spectra for micro-Raman spectroscopy, Thorlabs Inc He–Ne laser, SpectraPro-500i Acton Research Corporation monochromator, Germanium detector.
4：Experimental Procedures and Operational Workflow:
After thermal cleaning, a crystalline Al thin film of 30 s was deposited over the substrate at a growth temperature (Tg) of 850 ?C. Subsequently, the N-plasma source was ignited at 150 W with a N2 flow of 0.25 sccm. Then, an AlN layer was formed by 6.5 min of unintentional nitridation of the Al layer. The next step consisted of depositing an AlN layer for 30 min at a temperature Tg of 850 ?C. Finally, for the growth of the InN, the temperature Tg was lowered down to 400 ?C.
5：25 sccm. Then, an AlN layer was formed by 5 min of unintentional nitridation of the Al layer. The next step consisted of depositing an AlN layer for 30 min at a temperature Tg of 850 ?C. Finally, for the growth of the InN, the temperature Tg was lowered down to 400 ?C.
Data Analysis Methods:
5. Data Analysis Methods: The structural properties of the InN NCs were evaluated by HR-XRD. The surface morphology was analyzed by SEM. The nanocolumns were additionally studied by HR-TEM images. Micro-structural properties were studied by micro-Raman spectroscopy. The optical properties were obtained by the photoluminescence technique at 20 K and photoreflectance measurements.
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