Chemical Vapour Deposition of sp2 Hybridised Boron Nitride

Abstract

The aim of this work was to develop a chemical vapour deposition process and understand the growth of sp 2 hybridised Boron Nitride (sp 2 -BN). Thus, the growth on different substrates together with the variation of growth parameters was investigated in details and is presented in the papers included in this thesis. Deposited films of sp 2 -BN were characterised with the purpose to determine optimal deposition process parameters for the growth of high crystal quality thin films with further investigations of chemical composition, morphology and other properties important for the implementation of this material towards electronic, optoelectronic devices and devices based on graphene/BN heterostructures.For the growth of sp 2 -BN triethyl boron and ammonia were employed as B and N precursors, respectively. Pure H 2 as carrier gas is found to be necessary for the growth of crystalline sp 2 -BN. Addition of small amount of silane to the gas mixture improves the crystalline quality of the growing sp 2 -BN film.It was observed that for the growth of crystalline sp 2 -BN on c-axis oriented -Al 2 O 3 a thin and strained AlN buffer layer is needed to support epitaxial growth of sp 2 -BN, while it was possible to deposit rhombohedral BN (r-BN) on various polytypes of SiC without the need for a buffer layer. The growth temperature suitable for the growth of crystalline sp 2 -BN is 1500 °C. Nevertheless, the growth of crystalline sp 2 -BN was also observed on -Al 2 O 3 with an AlN buffer layer at a lower temperature of 1200 °C. Growth at this low temperature was found to be hardly controllable due to the low amount of Si that is necessary at this temperature and its accumulation in the reaction cell. When SiC was used as a substrate at the growth temperature of 1200 °C, no crystalline sp 2 -BN was formed, according to X-ray diffraction.Crystalline structure investigations of the deposited films showed formation of twinned r-BN on both substrates used. Additionally, it was found that the growth on Om man skulle kunna göra ljusdioder av BN skulle dessa sända ut ljus med en våglängd på cirka 220 nm alltså den typen av ultraviolettljus (UV) som ozonlagret filtrerar bort från solen. Av sådana ljusdioder skulle man sedan kunna göra vita ljusdioder genom att använda en luminofor, vilket är ett material som absorberar UV-ljus och sedan sänder ut vitt ljus, men ännu mera spännande skulle det vara att använda ljusdioderna för vattenrening då denna typ av UV-ljus dödar bakterier.Eftersom BN bildar samma kristallstrukturer som kol, så är den grafitlika, sp 2 -hybridiserade formen av BN mycket intressant att använda tillsammans med grafen.Beräkningar har visat att om man använder sp 2 -BN som substrat till grafen så kommer man åt större del av de förutspådda materialegenskaperna för grafen än om man använder andra substrat.Syftet med detta arbete har varit att utveckla en syntesprocess för tunna filmer av sp 2 -BN med tillräckligt hög kvalité för att kunna börja utforska alla möjligheter med BN, för detta har en teknik som kal...