Determination of carrier lifetime and diffusion length in Al-doped 4H-SiC epilayers by time-resolved optical techniques

• Published in: Journal of physics. D, Applied physics Applied physics, 2015-01, Vol.48 (2), p.25103-7
• Main Authors: Liaugaudas, Gediminas, Dargis, Donatas, Kwasnicki, Pawel, Arvinte, Roxana, Zielinski, Marcin, Jaraši nas, K stutis
• Format: Article
• Language: English
• Subjects: Al-doped 4H-SiC; Aluminium; Aluminum; Ambipolar diffusion; Asymptotic properties; Carrier lifetime; Coefficients; Diffusion coefficient; Diffusion length; Minority carriers; time-resolved optical techniques
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/0022-3727/48/2/025103

A series of p-type 4H-SiC epilayers with aluminium concentration ranging from 2  ×  1016 to 8  ×  1019 cm−3 were investigated by time-resolved optical techniques in order to determine the effect of aluminium doping on high-injection carrier lifetime at room temperature and the diffusion coefficient at different injections (from 3  ×  1018 to 5  ×  1019 cm−3) and temperatures (from 78 to 730 K). We find that the defect limited carrier lifetime τSRH decreases from 20 ns in the low-doped samples down to 0.6 ns in the heavily doped epilayers. Accordingly, the ambipolar diffusion coefficient decreases from Da = 3.5 cm2 s−1 down to 0.6 cm2 s−1, corresponding to the hole mobility of µh = 70 cm2 Vs−1 and 12 cm2 Vs−1, respectively. In the highly doped epilayers, the injection-induced decrease of the diffusion coefficient, due to the transition from the minority carrier diffusion to the ambipolar diffusion, provided the electron diffusion coefficient of De 3 cm2 s−1. The Al-doping resulted in the gradual decrease of the ambipolar diffusion length, from LD = 2.7 µm down to LD = 0.25 µm in the epilayers with the lowest and highest aluminium concentrations.