Fabricating And Improvement Of GaAs Pyramidal Microtips

Scanning near-field optical microscopy(SNOM for short) is a novel and quick developing tool in the recent several decades.It uses the evanescent field confined at the tiny aperture to provide images of rough surfaces with a resolution beyond the classical optical diffraction limit,and can be down to nanometer scale.And it will have great influences not only in the fields of physics,chemistry,biology,material science,microelectronics and so on,but also in medicine and information technology.One of the most important potential applications can be found in the ultra-high density optical data storage.Therefore,to realize this application,a promising architecture of monolithic integrated SNOM sensor has been proposed.The sensor is composed of a GaAs pyramidal microtip,a vertical-cavity surface-emitting laser(VCSEL) cavity and a pin monitor.Since microtip is one essential part of SNOM,the fabrication of high quality GaAs pyramidal microtips has become a key matter.In this paper,the technology of fabricating GaAs pyramidal microtips by selective Liquid Phase Epitaxy is introduced in great details,including mask preparation,photolithography, wet etching and liquid phase epitaxial growth.We use two different kinds of graphite boats to grow the GaAs pyramidal microtips by changing the methods of the growth solution separating off the GaAs substrate:by using the traditional horizontal graphite boat,the growth solution separates off the GaAs substrate by the horizontal pushing the growth solution after the growth of the GaAs pyramidal microtips;while by using the rotary graphite boat,the growth solution separates off the GaAs substrate by the gravity when rotating the rotary graphite boat by 180°.Scanning electron microscopy(SEM) images show that,compared to the GaAs pyramidal microtips grown by the horizontal graphite boat,the quality of the GaAs pyramidal microtips grown by the rotary graphite boat is improved.The achievement introduced here represents an important step towards the application of scanning near-field optical microscopy sensor.