Fabricating Vertical Sidewalls in GaAs∕AlGaAs Heterostructure Using Light-Induced Wet Etching

Abstract

We investigate the effects of light-induced wet etching ͑LIWE͒ on sidewall profile and etch rate for n-and p-type GaAs bulk, epitaxial AlGaAs layers and two different types of laser heterostructure using three different etch masks and three light-emitting diodes as light sources. The experiments show that the LIWE parameters ͑light-source wavelength, mask conductivity, sample layer structure͒ control the sidewall angle and etch rate. The technique successfully produced vertical sidewalls and "on-demand" etch-stop layers in laser heterostructure using sulfuric acid ͑H 2 SO 4 ͒: hydrogen peroxide ͑H 2 O 2 ͒: DI water ͑H 2 O͒ etch system. Wet etching has potential advantages over dry etching, 1-3 including lower cost, smoother surfaces, and larger etch rates. Integrated devices require a variety of etched-sidewall profiles and angles ranging from shallow etched-slopes for electrical contacts to vertical flat smooth surfaces for integrated laser mirrors. Vertical etches must maintain good control of lateral etching to inhibit smoothing of patterned features, prevent undercutting of metal contacts, and to increase the degree of integration for some types of devices including micro-optical-electrical-machines ͑MOEMs͒ with close-fitting moveable parts. 4 The sidewall profiles obtained from wet chemical etching normally depend on the etching solution and the material crystal direction. 5-8 Light-induced wet etching ͑LIWE͒ 9 potentially expands the fabrication options offered by anisotropic dry etching by using light to break the normal crystal-plane etching and thereby provides control over the sidewall profiles with angles ranging from several degrees to 90 degrees while retaining many favorable wetetching properties.The present research investigates the effects of LIWE on sidewall profiles and etch rate for n-and p-type GaAs bulk, epitaxial AlGaAs layers, and two different types of laser heterostructure with three different etch masks. The sidewall angle and etch rate are controlled by the etch condition including wavelength of the light source, electrical property of the mask, and layer structure of the material. The results show that a judicious choice of wavelength during the LIWE of heterostructure can transform a normally etching layer into an etch-stop layer or alter the etched-sidewall angle. The LIWE experiments reported here have successfully etched a vertical sidewall in laser heterostructure material.Photochemical etching has many possible applications such as maskless etching, selective etching, and control of the etched side wall profile. Podlesnik et al. 10 show that laser light increases the etch rate in illuminated regions of the sample. Deep trenches in n-type GaAs and AlGaAs have been fabricated by applying a focused laser beam 10-12 directly to a bulk sample positioned within the etching solution. Van de Ven et al. 13 fabricate square contours on GaAs samples by scanning a laser beam in a square pattern. The technique gives rise to the possibility of maskless etching whereby accurate control of the ...

Realization of smooth side profile using diffusion-controlled wet chemical etching for HgTe/(Hg,Cd)Te heterostructures

“…In this connection, it has been proposed that the side profile of semiconductor heterostructures is mainly influenced by the charge carrier concentration in the various layers in the layer stack [13]. Further factors considered for achieving smoother side profiles include modification in wet etchant composition, optimising etching conditions such as temperature, the viscosity of the etchant and its agitation [14], as well as etch mask conductivity [15].…”

Kinetic Investigation on the Photoetching Reaction of n-Type GaAs by Scanning Electrochemical Microscopy

“…19,20 In semiconductor manufacture, the challenge is to control the photoetching process with a micro-and nanometer accuracy. Both focused laser beam 7,9,21,22 and light mold 8,11,12 are adopted for this purpose. However, the working electrolytes usually contain strong oxidants with strong acid [7][8][9]11,23 or alkali environment, 12,24,25 e.g., the H 2 O 2 /H 2 SO 4 solution, in which the semiconductor materials can be spontaneously corroded.…”

“…When the semiconductor is illuminated, the charge separation results in local bipolarity. In the presence of appropriate electrolyte, the photogenerated holes would oxidize the reductive species in solution − or the semiconductor itself if the photogenerated electrons were removed by electron acceptors. − On the basis of this photocorrosion phenomenon, photoetching techniques have been developed to fabricate three-dimensional micro- and nanostructures (3D-MNSs) directly on semiconductor wafers. − For example, porous silicon roughened by photoetching process can enhance light-harvesting efficiency and improve the photoelectric conversion efficiency. , …”

“…Both focused laser beam ,,, and light mold ,, are adopted for this purpose. However, the working electrolytes usually contain strong oxidants with strong acid − ,, or alkali environment, ,, e.g., the H 2 O 2 /H 2 SO 4 solution, in which the semiconductor materials can be spontaneously corroded. The methodologies of corrosion kinetics are also adopted to investigate the effects of light intensity, solution components and also dopants in semiconductors on the etching rates and profiles of etching pits. ,,− Nevertheless, the kinetic investigation on the interfacial charge transfer across the illuminated semiconductor/electrolyte interface has been seldom reported.…”

Wavelength dependent laser-induced etching of Cr-O doped GaAs: Morphology studies by SEM and AFM

“…Laser-induced etching, an improved etching process, is very much needed in the fabrication of III-V integrated optic and microelectronic devices (Syvenkyy et al 2005;Veiko et al 2005;Yi and Parker 2006). Several studies of laser induced etching have shown the importance of its higher processing rate than the conventional etching techniques (Svorcik and Rtybka 1989;Cha et al 1997;Han et al 1998;Simkiene et al 2003).…”