Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

RECOMBINATION AND DIFFUSION PROCESSES IN ELECTRONIC GRADE 4H SILICON CARBIDE
Patrik Ščajev^a, Liudvikas Subačius^b, Kęstutis Jarašiūnas^a, and Masashi Kato^c,d
^aInstitute of Photonics and Nanotechnology, Vilnius University, Saulėtekio 3, 10257 Vilnius, Lithuania
^bCenter for Physical Sciences and Technology, Saulėtekio 3, 10257 Vilnius, Lithuania
^cDepartment of Engineering Physics, Electronics and Mechanics, Nagoya Institute of Technology, Nagoya 466-8555, Japan
^dFrontier Research Institute for Materials Science, Nagoya Institute of Technology, Nagoya 466-8555, Japan
E-mail: liudvikas.subacius@ftmc.lt
Received 15 October 2018; revised 6 December 2018; accepted 2 January 2019

Carrier dynamics in n-type 4H-SiC epilayers of varying thicknesses and low Z_1/2 defect concentrations are investigated here in wide ranges of excess carrier density and temperature. Several techniques are employed to monitor carrier diffusion and recombination processes, including light induced transient grating (LITG), microwave photoconductance decay (MPCD) and free carrier absorption (FCA) using ps-laser pulses at 355 nm. The observed increase of the diffusion coefficient with the increasing excitation level is explained by the transition from the minority to the bipolar transport regime. Its subsequent decrease with even higher excitations is found to be governed by band-gap renormalization and degeneracy effects. The bulk lifetime, limited by hole traps at 0.19–0.24 eV above the valence band at lower excitations, was found to decrease from few microseconds to hundreds of nanoseconds during the transition regime from the minority to the bipolar transport. Our temperature-dependent measurements confirmed the trap activation energy and provided the approximate functional form of electron and hole lifetimes as τ_e = 340 × (T/300 K)^3/2 ns and τ_h = 100 × (T/300 K)^–1/2 ns, for the temperature T range 80–800 K. It was found to hold for 65 and 120 μm sample thicknesses, while the lifetimes were found to be twice shorter for the sample 35 μm thick.

Keywords: silicon carbide, microwave photoconductance, free carrier absorption, transient grating, lifetime
PACS: 72.20.Jv, 72.40.+w

REKOMBINACIJOS IR DIFUZIJOS PROCESAI ELEKTRONINĖS KOKYBĖS 4H SILICIO KARBIDE
Patrik Ščajev^a, Liudvikas Subačius^b, Kęstutis Jarašiūnas^a, Masashi Kato^c,d

^aVilniaus universiteto Fotonikos ir nanotechnologijų institutas, Vilnius, Lietuva
^bFizinių ir technologijos mokslų centras, Vilnius, Lietuva
^cNagojos technologijos institutas, Nagoja, Japonija

Darbe tiriama krūvininkų dinamika jų tankio 10¹⁴ –10¹⁸ cm^–3 ir temperatūros 80–800 K intervaluose fotosužadintuose n-tipo 4H-SiC sluoksniuose, 35, 65 ir 120 μm storio, legiruotuose 10¹⁵ cm^–3 tankio azoto priemaišomis bei turinčiuose mažą Z_1/2 defektų tankį. Šviesa indukuotų dinaminių gardelių, mikrobangų fotolaidumo bei laisvųjų krūvininkų sugerties metodikos buvo pritaikytos krūvininkų rekombinacijos ir difuzijos vyksmų tyrimams, naudojant sužadinimui pikosekundinio Nd:YAG lazerio impulsus, esant 355 nm bangos ilgiui. Krūvininkų difuzijos koeficiento didėjimas, nustatytas intensyvinant žadinimą, buvo paaiškintas pernašos mechanizmų kaita, monopolio transporto virsmu bipoliu. Stipraus žadinimo atveju gautas difuzijos koeficiento sumažėjimas buvo priskirtas daugiadalelei sąveikai bipolėje plazmoje: energijos juostų renormalizacijai ir išsigimimui. Be to, intensyvinant žadinimą, buvo nustatyta, kad trumpėja krūvininkų gyvavimo trukmė (nuo kelių mikrosekundžių iki šimtų nanosekundžių). Trumpėjimas buvo paaiškintas skylių gaudyklių (lygmuo ties E_V + 0,19–0,24 eV) įtaka bei bipolės pernašos mechanizmų fotosužadintame 4H-SiC kaita. Atlikti temperatūriniai laisvųjų krūvininkų sugerties tyrimai patvirtino mūsų modeliniuose skaičiavimuose panaudotą gaudyklių aktyvacijos energijos vertę bei leido nustatyti elektronų ir skylių gyvavimo trukmių temperatūrines priklausomybes.

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