Showing papers by "Shizuo Fujita published in 2001"
TL;DR: In this article, a homoepitaxially grown ZnO by metal-organic vapor phase epitaxy (MOVPE) on molecular beam epitaxy-grown ZnOs layers after pretreatment of the underlying MBE-ZnO at 1000°C in N2 resulted in an atomically flat surface.
Abstract: Zinc oxide (ZnO) of high quality was homoepitaxially grown by metal-organic vapor phase epitaxy (MOVPE) on molecular beam epitaxy (MBE)-grown ZnO layers after the pretreatment of the underlying MBE-ZnO at 1000°C in N2 which resulted in an atomically flat surface. In photoluminescence at 15 K, the 3 meV line width of the emission from donor-bound-excitons (D0X) and the observation of the fourth phonon replica of the emission from free-excitons (EX) have demonstrated the high potential of MOVPE growth of ZnO toward optical applications.
77 citations
TL;DR: In this article, the best quality of h-GaN is obtained on (114)B, where the crystallographic relationship is found from a pole figure to be h-gaN{0001}‖GaAs(335)B and h-gnaN{1012}
Abstract: Hexagonal GaN (h-GaN) layers are grown by metalorganic vapor-phase epitaxy on GaAs{11n}A and B (n=8, 4, 3, 2, 1) substrates using AlAs intermediate layers. The best quality of h-GaN is obtained on (114)B, where the crystallographic relationship is found from a pole figure to be h-GaN{0001}‖GaAs(335)B and h-GaN{1012}‖GaAs(001). We propose a simple model that explains why such a crystallographic relationship is easily realized on {114} resulting in the superior structural and optical properties. Furthermore, from a comparison between the growth on the A and B substrates, it is pointed out that the polarity is a key factor in determining the crystallographic properties.
7 citations
TL;DR: In this article, the authors discuss the problem of HOMO and LUMO and propose a method to solve it: "HOMO" and "LUMO".
Abstract: 本稿では, 有機薄膜のHOMOおよびLUMO準位をそれぞれ半導体の価電子帯, 導電帯に対応させることにより, 半導体多層構造におけるタイプI, タイプIIの概念をほぼ等価に有機薄膜マルチ構造に対して用いることが出来ることを実験的に示した.界面でのキャリア注入等, 半導体のバンド構造と等価に考えてよいかといった問題は未だあるが, 少なくとも発光デバイスに関して有機薄膜マルチ構造を用いることにより発光効率の向上が期待される.したがって, HOMO, LUMO準位をもとにした構造設計により, 高機能・新機能デバイスの発現につながりうるであろうと期待される.他方, 成膜技術の観点で見ると, nmレベルでの界面・膜厚の制御, 分散膜にあっては組成の制御が必要である.原料セルの温度は200℃以下で正確に制御する必要があり, 成長中その場での表面観察やnmレベルでの成膜速度の測定など, 半導体の分子線エピタキシ (MBE) 技術の延長にはない有機薄膜特有の技術が求められるであろう.特にMBEにおける反射電子線回折 (RHEED) とその振動による膜厚制御という, 半導体において成長膜の特性と構造制御にとって不可欠な技術が, 非晶質で分子間結合の弱い有機薄膜の成膜には用いることが困難である.RHHEDに代わるようなその場観察技術や, 成長機構の解明による単分子層レベルでの成膜・膜厚制御技術の確立が求められるとともに, 非晶質である有機薄膜の配向を単分子層レベルで制御してゆくような成膜技術を開拓してゆく必要があると思われる.
TL;DR: In this article, a rule for designing white electroluminescence (EL) spectra is discussed in terms of the multilayer structures and a structure for designing the white luminescence is discussed.
Abstract: White electroluminescence (EL) spectra are carefully investigated in terms of the multilayer structures and a rule for designing the white luminescence is discussed. For a simple structure which consists of tris(8-hydroxyquinoline)-aluminum (Alq) and 1, 2, 3, 4, 5-pentaphenyl-1, 3-cyclopendadiene (PPCP) emitting green and blue luminescence, respectively, as luminescent and electron transport layers, white luminescence appeared if the thickness of each layer was appropriately chosen. The luminescence efficiency was higher in PPCP, and therefore one of the structures effectively emitting white luminescence was designed as PPCP(10 nm)/Alq(40 nm). The 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) was then added to the PPCP/Alq structure intending to enhance red luminescence. We propose the structure where red luminescence is from the DCM as photoluminescence excited by the green and blue luminescence from Alq and PPCP, which was effective, compared to the PPCP/Alq/DCM stacking structure, in avoiding increase of the operating voltage. The importance of designing structures of organic white EL devices based on fundamental optical properties of the constituent layers and on luminescence dynamics is highlighted.