Conventional thermal annealing for a more efficient p-type doping of Al + implanted 4H-SiC
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Anders Hallén KTH Royal Institute of Technology, School of Information and Communication Technology (School of ICT), SE-164 40, Kista-Stockholm, Sweden
Antonella Parisini Università di Parma, CNISM - Dipartimento di Fisica, I-43124 Parma, Italy (Received 29 March 2012; accepted 1 June 2012)
The p-type doping of high purity semi-insulating 4H polytype silicon carbide (HPSI 4H-SiC) by aluminum ion (Al1) implantation has been studied in the range of 1 1019 to 8 1020 /cm3 (0.39 lm implanted thickness) and a conventional thermal annealing of 1950 °C/5 min. Implanted 4H-SiC layers of p-type conductivity and sheet resistance in the range of 1.6 104 to 8.9 102 Xu, corresponding to a resistivity in the range of 4.7 10 1 to 2.7 10 2 X cm have been obtained. Hall carrier density and mobility data in the temperature range of 140–720 K feature the transition from a valence band to an intraband conduction for increasing implanted Al ion concentration from 1 1019 /cm3 to 4 1020 /cm3. A 73% electrical activation, 31% compensation and 146 meV ionization level have been obtained using a best-fit solution of the neutrality equation to Hall carrier data for the lowest concentration.
I. INTRODUCTION
Selective area doping of silicon carbide (SiC) by ion implantation is still the preferred technology for the fabrication of heavily doped n- and p-type regions in SiC electronic devices to reduce the specific resistance of a metal contact. Moreover, the more elevated doping values achievable by ion implantation with respect to epitaxial growth might favor the carrier emitter efficiency in bipolar devices under heavy current injection. The atomic solid solubility of dopant species in a SiC lattice sets the upper limit for the incorporation of such a species in SiC as an electrical dopant. N-type and p-type dopant solubility in SiC has been established in epitaxial material and these values constitute the upper boundaries, which need to be reached or overpassed to further increase the active doping concentration in the case of ion-implanted SiC materials. To obtain this, both the implanted dopant concentration per unit volume, as well as the temperature of the mandatory postimplantation annealing process for the recovery of the ion-damaged SiC lattice and the electrical activation of the implanted species, have been increased over the years.
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.207 J. Mater. Res., Vol. 28, No. 1, Jan 14, 2013
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The most used n-type dopants in SiC are nitrogen (N) and phosphorus (P). N and P occupy closely spaced levels in the 4H-SiC band gap, with N slightly deeper than P.1 Unfortunately, there exists a discrepancy between experimental values regarding the solid solubility of N and P in epitaxial SiC materials, whereas in the case of ionimplanted SiC the published results agree on the fact that N electrical activation saturates at lower concentrations than P.2,3 In particular, for 4H-SiC the elect
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