Maskless micro/nanofabrication on GaAs surface by friction-induced selective etching
© Tang et al.; licensee Springer. 2014
Received: 7 January 2014
Accepted: 28 January 2014
Published: 4 February 2014
In the present study, a friction-induced selective etching method was developed to produce nanostructures on GaAs surface. Without any resist mask, the nanofabrication can be achieved by scratching and post-etching in sulfuric acid solution. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Results showed that the height of the nanostructure increased with the normal load or the etching period. XPS and Raman detection demonstrated that residual compressive stress and lattice densification were probably the main reason for selective etching, which eventually led to the protrusive nanostructures from the scratched area on the GaAs surface. Through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters. In summary, the proposed method provided a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface.
KeywordsMaskless Micro/nanofabrication GaAs Friction-induced selective etching
Due to its direct bandgap and high electron mobility, gallium arsenide (GaAs) has become one of the most widely used compound semiconductor materials. For instance, GaAs is the perfect substrate for quantum luminescent devices, such as photoelectric detector , high-performance laser , quantum information processing , and so on. Nevertheless, the precondition for realizing these quantum devices is to grow quantum dots on certain positions of substrate [4, 5]. Thus, the controllable fabrication of the patterned GaAs substrate is a significant issue of concern.
Many efforts have been made in producing patterned GaAs substrate. As a prevalent technology, the photolithography has been used for the fabrication on GaAs surface . However, the conventional photolithography has the embarrassment in its resolution vs. cost, i.e., the production cost will be much higher as the resolution is improved . Although the electron beam (EB)  and focused ion beam (FIB)  lithography technology can enable higher machining precision and finer resolution patterning, these techniques are costly and complex, requiring multiple-step processes . In addition, anodic oxidation has been demonstrated the potential in the creation of structures, patterns, and devices at the nanometer scale , but the operation will be controlled under rigorous environmental requirements, such as applied voltage, suitable humidity, and so on . Such processes can also bring contamination and impurity onto the area fabricated . In recent decades, the proximal probe method based on the mechanical stamp and scratching technique has been employed to produce patterned GaAs substrate [4, 14], but it is difficult, if not impossible, to fabricate GaAs nanostructures with low destruction by solely mechanical scratching. Therefore, it is necessary to develop a straightforward and more flexible fabrication method for the GaAs surface.
In the present study, a novel friction-induced micro/nanofabrication method that consists of nanoscratching and post-etching was presented to produce nanostructures on GaAs. The effects of the applied normal load and etching period on the formation of the nanostructure were studied. Based on the X-ray photoelectron spectroscope (XPS) and Raman spectra characterization, the fabrication mechanism of the nanostructure was discussed. Finally, through a homemade multi-probe instrument, the capability of this fabrication method was demonstrated by producing various nanostructures on the GaAs surface, such as linear array, intersecting parallel, surface mesas, and special letters.
The GaAs (100) wafers, n-doped with Si, were purchased from JMEM Electronic Materials, Ltd., Tianjin, China. Using an atomic force microscope (AFM, SPI3800N, Seiko, Tokyo, Japan), the surface root-mean-square (RMS) roughness of the GaAs wafer was measured as 0.5 nm over a 1 μm × 1 μm area. The crystal state of the GaAs material was detected by the X-ray diffraction (XRD, X'Pert, PANalytical, Almelo, Netherlands), showing that the GaAs wafer was single crystal in (100) plane orientation. Before the fabrication, the GaAs wafers were ultrasonically cleaned with methanol and ethanol for 3 min in turn, and successively rinsed with deionized water for 10 min to remove surface contamination.
XPS and Raman characterization
In order to investigate the mechanism of the friction-induced selective etching process, the mesas with an area of 500 μm × 500 μm and a height of 60 nm were prepared by the homemade multi-probe instrument under a normal load of 10 mN and post-etching for 30 min. The chemical state of the fabrication area on the GaAs surface was detected by an XPS (Thermo VG250, Thermo, Waltham, MA, USA). The microstructure of the fabrication area on the GaAs surface was measured using a Raman spectrometer (RM2000, Renishaw, Gloucestershire, UK). The excitation was supplied by the 514.5 nm Ar+ ion laser. To avoid the random error in detection, each sample was scanned for three times.
Results and discussion
Fabrication of GaAs nanostructures
Effect of etching period on friction-induced selective etching
Effect of normal load on friction-induced selective etching
Mechanism of the friction-induced selective etching on GaAs surface
Effect of surface oxide on the friction-induced selective etching
Effect of structural deformation on the friction-induced selective etching
Fabrication of surface pattern on GaAs surface
In summary, the present study proposed a friction-induced selective etching method on GaAs surface. XPS and Raman detection demonstrated that the residual compressive stress and the lattice densification was the main reason for the selective etching. Various patterns can be created on a target GaAs surface. Without any resist mask and applied voltages, this method provides a straightforward and more maneuverable micro/nanofabrication method on the GaAs surface.
Nanostructures can be created on the GaAs surface after scratching and post-etching in H2SO4 solution. The height of the nanostructures increased gradually with the increase in applied normal load or etching period.
Based on the XPS and Raman detection, it was found that the residual compressive stress and lattice densification induced by the scratching process were probably the main reason for the friction-induced selective etching.
Various nanostructures including line arrays and nanopatterns can be produced on the GaAs surface by the controlment of normal load, scanning trace, and etching period. Without any resist mask and applied voltages, the proposed method will open new opportunity for the micro/nanofabrication of GaAs.
atomic force microscope
focused ion beam
X-ray photoelectron spectroscope
The authors would like to thank Prof. Zhiming Wang and Prof. Jiang Wu from the University of Electronic Science and Technology of China for their useful discussions. The authors are grateful for the support from the Natural Science Foundation of China (91323103 and 51305365) and from the Specialized Research Fund for the Doctoral Program of Higher Education of China (20130184120008).
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