Photoemission study of 6H-SiC(000-1) reconstructed surface

Abstract

The polytype of 6H-SiC crystal in variety of polytype SiC has two polar surfaces perpendicular to (0001)Si and (000-1)C surfaces. In this paper, the electronic properties of 6H-SiC(000-1)C surfaces have been studied by AES (Auger Electron Spectroscopy), LEED (Low Energy Electron Diffraction) and PES (Photoemission Spectroscopy). A prepared sample was n-type 6H-SiC single crystal wafers with the carrier concentration of 2 x 10(exp 18)/cu cm. The samples have been treated in UHV (Ultra High Vacuum) system, then they have been annealed in situ by resistive heating. The (square root of 3) x (square root of 3) and 3 x 3 LEED pattern were observed after heating at 850 C and 900 C. It was found from Si(2p) spectra measurements for different annealing temperatures that the surface of 6H-SiC sample became clean at 900 C. Valence band photoemission spectra measured for 6H-SiC(000-1)C 3 x 3 reconstructed surface were shown in a figure. It was considered from the figure that the photoemission feature originated from surface states, because this feature located in the band gap energy region and did not disperse significantly with incident photon energy. And, the exact position of the valence band maximum could not determine from the spectra. It was suggested that the 3 x 3 reconstructed surface had semiconductive property.

SiCポリタイプの中で6H-SiC結晶は(0001)Si面と(000-1)C面に垂直な2つの極性面を持っている。本論文では、6H-SiC(000-1)C面の電子特性をAES(オージェ電子分光法)、LEED(低速電子線回折)およびPES(光電子放出分光法)を用いて研究した。キャリア濃度が2×10(exp 18)/立方センチメートルのn-型6H-SiC単結晶ウエハの試料を調製した。UHV(極高真空)装置で試料を処理し、次いで抵抗加熱方式を用いてその場で焼鈍した。850度Cおよび900度Cでの加熱後(√3×√3)と(3×3)LEEDパターンを観察した。異なる焼鈍温度に対するSiの2p測定値から6H-SiC試料表面は900度Cで清浄になることが分かった。6H-SiC(000-1)C 3×3再構成表面について測定した価電子帯光電子放出スペクトルを図示した。図から、光電子放出の特徴がバンド間隙領域にあり、入射光子エネルギー変化に伴う分散が有意的でなかったので、この特徴は表面状態から生じたものであると推察した。また、スペクトルから価電子帯極大の正確な位置を決定できなかった。(3×3)再構成表面が半導体性の性質を有していることを示唆した。