Sains Malaysiana 37(3): 265-269(2008)

Effects of Hydrogen and Helium Dilution on the Optical Band
Gap and Photoluminescence of DC PECVD Hydrogenated
Amorphous Carbon Films
(Kesan Penambahan Gas Hidrogen dan Helium ke atas Jurang Tenaga dan Fotoluminesen
Terhadap Filem Karbon Amorfus Berhidrogen PECVD Arus Terus)

Rozidawati Awang
School of Applied Physics
National University of Malaysia (UKM)
43600 Bangi, Selangor, Malaysia

Saadah A. Rahman
Solid State Research Laboratory
Physics Department, University of Malaya
50603 Kuala Lumpur, Malaysia

Received: 12 June 2007 / Accepted: 4 December 2007

ABSTRACT

A series of hydrogenated amorphous carbon (a-C:H) thin films were deposited using home-built direct-current (DC) plasma enhanced chemical vapour deposition (PECVD) system. In this present study, the a-C:H thin films were deposited using pure methane (CH4) gas diluted either with hydrogen (H) or helium (He). The effects of hydrogen and helium dilution on the photoluminescence (PL) properties and optical band gap (E04) were studied. The dependence of PL properties and optical energy gap on the film thickness has also been investigated. The characterization techniques used were optical transmission and photoluminescence spectroscopies. The sp2 cluster sizes were determined from Raman spectra are in the range of 5 to 7 nm. Hydrogen and helium dilution of methane strongly influences the PL efficiency of the a-C:H films. The PL efficiency are enhanced with increase in film thickness for a-C:H films prepared both from H and He diluted CH4. The optical energy gap of these films decreases with increase in H or He dilution and film thickness.

Keywords: hydrogenated amorphous carbon; hydrogen and helium dilution; PL; optical band gap

ABSTRAK

Suatu siri filem nipis karbon amorfus berhidrogen (a-C:H) disediakan menggunakan sistem Pemendapan Wap Kimia secara Peningkatan Plasma oleh arus terus (DC PECVD) yang dibina di makmal. Di dalam kajian ini, filem nipis (a-C:H) dimendapkan menggunakan gas metana (CH4) yang dicampurkan dengan gas hidrogen, (H) atau gas helium, (He). Kesan daripada percampuran gas ini terhadap sifat fotoluminesen (PL) dan nilai jurang tenaga (E04) dikaji. Kebergantungan sifat fotoluminesen dan nilai jurang tenaga kepada ketebalan filem turut dikaji. Teknik-teknik pencirian yang digunakan adalah spektroskopi transmisi optik dan spektroskopi fotoluminesen. Saiz kluster sp2 yang di perolehi daripada spektrum spektroskopi Raman adalah dalam julat 5 hingga 7 nm. Penambahan gas hidrogen dan gas helium dilihat amat mempengaruhi kecekapan fotoluminesen. Kecekapan fotoluminesen juga didapati bertambah apabila ketebalan filem bertambah untuk kedua-dua keadaan penyediaan, sama ada penambahan gas hidrogen atau gas helium kepada gas methane. Nilai jurang tenaga bagi kedua-dua jenis filem ini mengecil dengan penambahan gas hidrogen atau gas helium kepada gas metana dan pertambahan ketebalan filem.

Kata kunci: karbon amorfus berhidrogen; penambahan gas hidrogen atau gas helium; fotoluminesen; jurang tenaga optik

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