Ion Beam Induced Regrowth in GaAs
- PDF / 635,840 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 114 Downloads / 218 Views
ION BEAM INDUCED REGROWTH IN GaAs S.T. JOHNSON, J.S. WILLIAMS, E. NYGREN and R.G. ELLIMAN1 RMIT Microelectronics Technology Centre, Melbourne, Australia 1CSIRO Materials Science and Technology, Clayton, Australia ABSTRACT Ion implanted, amorphous layers on (100) GaAs have been recrystallised epitaxially by 1.5 MeV Ne÷ irradiation at temperatures between 750C and 1350C. The extent of regrowth essentially increases linearly with ion fluence in the early stages of crystallization and the process is characterized by an activation energy of 0.16eV, about an order of magnitude lower than that for thermal - only epitaxy. Beam annealing produces dislocations in the underlying GaAs crystal, the density of which increases with depth up to the Ne÷ ion range. INTRODUCTION Amorphous Si layers recrystallize epitaxially from underlying crystalline material when heated to temperatures above about 4500C, with an activation energy of - 2.7 eV [1]. Amorphous GaAs layers also recrystallize epitaxially but at somewhat lower temperatures, above about 200 0C. However, with GaAs the regrowth rates are decidedly non-linear and the regrown layers are usually highly defective [2]. Recent experiments have demonstrated that epitaxial crystallization can be induced in amorphous Si at relatively low temperatures (- 200-4000C) by ion irradiation [3]. This process was found to be weakly temperature dependent exhibiting an activation energy of 0.24eV, a value which is approximately an order of magnitude lower than that found for thermally induced epitaxy. Preliminary measurements have also indicated that ion beam induced epitaxial crystallization of amorphous GaAs layers can be observed at temperatures below about 100oC [4]. Fig. 1 schematically depicts this process. The kinetics of ion beam induced epitaxy and the microstructures of the crystallized material are the subject of the present study.
a) Initial State.
1
a-GaAs
b) Crystallization.
'"-
MeV ions
Mat. Res. Soc. Symp. Proc. Vol. 100. ©1988 Materials Research Society
Schematic SFigurerepresentation of experimental conditions for ion-beam induced epitaxy in GaAs.
424
EXPERIMENTAL Single crystal GaAs wafers were cooled to 400 0 C, but even under these conditions, epitaxy is severely disrupted leaving a residual damaged layer consisting of heavily twinned crystal, behaviour which is consistent with previous studies [5]. The RBS-C spectra in Fig. 2 illustrate ion-beam-induced epitaxial crystallization of amorphous GaAs layers. Fig. 2a shows the regrowth of an initially 320 Alayer as a function of fluence of 1.5 MeV Ne* ions at an irradiation temperature of 850C. The amorphous layer is shown to regrow - 30 X following a fluence of 2 x 1015 cm- 2, and continues to grow linearly with increasing ion fluence. The RBS spectra in Fig. 2b show epitaxial crystallization of an initially 230 A amorphous layer irradiated at 1000C. In this case the layer is observed to regrow to within - 90 A of the surface by a fluence of 8 x 1015 cm- 2. At this stage epitaxy appears to cease and continued irradi
Data Loading...
