Selective Suppression of Carrier-Driven Photochemical Etching: Raman Spectroscopy as a Diagnostic Tool
- PDF / 351,697 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 92 Downloads / 173 Views
SELECTIVE SUPPRESSION OF CARRIER-DRIVEN PHOTOCHEMICAL ETCHING: SPECTROSCOPY AS A DIACNOSTIC TOOL C. I. H. ASHBY, D. R. Myers, G. A. Vawter, R. M. BIEFELD, and J. Sandia National Laboratories, Albuquerque, New Mexico 87185
RAMAN
F.
KLEM
ABSTRACT Carrier-driven photochemical etching of semiconductors can be selectively suppressed by altering the near-surface region to enhance carrier recombination, thereby reducing the supply of carriers that drive the surface etching reaction. Two methods for enhancing recombination and decreasing the etch rate at a given phonon flux include ion implantation and localized Zn diffusion. Raman spectroscopy can be employed to determine whether sufficient alteration of electronic properties has occurred to suppress etching. Carrier-driven photochemical reactions, which require direct participation of free carriers for the chemical reaction to proceed, can be selectively suppressed by increasing the minority carrier recombination rate, thereby reducing the supply of carriers that drive the surface etching reaction. Two methods for enhancing recombination and decreasing the etching quantum yield, which is the number of atoms removed per incident photon, include ion implantation and localized Zn diffusion. For ion implantation, recombination-promoting defect concentrations depend on ion species, fluence, and annealing both during and after the implantation process. Other recombination processes related to carrier scattering from ionized impurities from in-diffusion of dopants or following implant activation can control etching. Raman spectroscopy can be employed to detect changes in electronic properties that correlate with etching suppression. Changes that occur in the LO-phonon lineshape, such as those associated with phonon confinement and ionized impurity scattering, can be diagnostic of the carrier-driven etching behavior following a specific treatment. We have demonstrated two applications of Raman spectroscopy as a diagnostic for suppression of the carrier-driven photochemical etching of GaAs. EXPERIMENT The substrate material for both implantation and Zn-diffusion treatments 7 3 was n-GaAs (100) with an impurity concentration of l.O±0.2xlO1 Si/cm . 11 Sam ples of this material were implanted with 40-keV B+ ions at fluences of 2 101O, 1012, and 1014 ions/cm . Other samples were type-converted to p - mid2 3 10 0/cm over a depth of about 1.2 om by closed-tube Zn diffusion (1). Diffusion was performed in a sealed quartz ampoule using elemental Zn and 17 18 3 As. Type-conversion to a lower Zn concentration (10 -10 /cm p-GaAs) by Zn diffusion in an MOCVD reactor under an AsH 3 overpressure (2) permitted comparison of the effects of low and high p-type impurity concentrations on etching quantum yields. The lower-concentration p-GaAs was type converted over a depth of approximately 200 nm. The Raman probe depth (26 rnm) was much shallowerer than the type-converted regions. All samples were photochemically etched under conditions that produce no measurable thermal etching of an untreate
Data Loading...
