High-Energy Ion-Implantation of a Moderately Deep Acceptor Hg Into Liquid Encapsulated Czochralski Grown GaAs : Formatio
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spectrometer and a Peltier-cooled GaAs photomultiplier as a detector [1-3]. For the measurements of deep emissions, a Ge detector was also used. Some samples were evaluated by Raman scattering and Rutherford backscattering spectroscopy (RBS). RESULTS AND DISCUSSION Electrical Properties The net hole concentration, INA-NI) of Hg+ ion-implanted GaAs as a function of [Hg] is shown in Fig.1. Open triangles and closed squares are INA-NDI for RTA- and FA- samples, respectively. For nearly the entire range of [Hg], INA-NDI of RTA-samples is 2 to 3 times larger than that of FA-samples. One should note that an activation rate as high as 30 % was obtained for 3 [Hg]=lxl01 9 cm- 3 with INA-NDI=3.0xl018 cm- . RBS results indicated that the diffused front of Hg atoms in RTA-samples is around 100nm from the surface, while it is about 150 nm in FAsamples. These observations imply that the diffusion of Hg atoms is more significant in FAsamples than in RTA-samples. The gradual decrease of INA-ND) for [Hg] at doses higher than ~Sx 1020 cm- 3 for both RTA- and FA-samples is ascribed to the uneliminated residual damage. Hall mobilities of Hg+ ion-implanted GaAs were compared with those of Be-doped GaAs prepared by MBE as a function of INA-NDI and they were found to be quite comparable [1,7].
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Figure 1. Net hole concentration, INA-NlJ as a function of Hg concentration, iHgI from 400keV Hg+ ion-implanted GaAs. Open triangles are for RTA samples while closed squares are for FA samples. 836
Photoluminescence Properties PL spectra of un-implanted and Hg+ ion-implanted LEC-GaAs samples annealed by FA are shown in Fig.2 as a function of [Hg]. The emission due to free excitons, FE, is seen with three carbon-related emissions, (C', X), (e, C) and (D, C). Here (C°, X) is the emission due to excitons bound to neutral C acceptors, (e, C) is that due to the transition from the conduction band to C acceptors and (D, C) is that due to the pairs between unidentified donors and C acceptors [1-3]. The un-implanted but annealed samples present PL features almost identical to the starting LEC-GaAs samples. By Hg doping at least seven emissions are formed with increasing [Hg]. An emission named [g-g] appears for [Hg]=3xl01 8 cm- 3 (INA-NDJ=5. 9 xl017 cm3 ) and displays a steep energy jump towards the higher energy for [Hgl=5x10 19 cm- 3 . For [Hgl>5xl0 19 cm- 3 (INANDJ>3,7xl01 8 cm- 3 ) , [g-g] appears as a broad emission at 1.507 eV and shows no energy shift with varying [Hg]. The conduction band to Hg acceptor transition, (e, Hg) is identified for [Hg] > lxO 18 cm"3 (for INA-NIl > 4.2x1017 cm- 3 ). The width of (e, Hg) is greatly broadened for increasing
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