Characteristics of ZnSe Films Grown by cw CO2 Laser with Ion Beam-assisted Deposition
|摘要:||我們使用離子輔助連續式二氧化碳雷射蒸鍍系統成長ZnSe薄膜在石英玻璃基與（100）砷化鎵基板上。薄膜在石英玻璃基板上為高度傾向方向排列的多晶zinc-blende結構，即使膜在溫下製成。在未加離子束輔助情況下，以蒸鍍速率6.4A/sec、基板溫度150℃製成的膜為最佳，其在波長700nm的折射率n=2.528、吸收消光係數k=0.0016，剝落度(peel strength) Fp=11.4mN。在有離子輔助的情況下，以離子束電壓200V、離子束電流15mA輔助製成的膜最佳，其在700nm波長的折射率n=2.536 逼近於單晶ZnSe塊材的值2.540、吸收消光係數k=0.0010，剝落強度Fp=16.9mN。由拉曼光譜分析得到ZnSe薄膜與石英玻璃基板間的應力x=1.27×1013 dyn cm-2。以此系統製備的多晶ZnSe薄膜在特性上的表現，優於以傳統熱蒸鍍與電子束蒸鍍所製備的膜。
在(100)砷化鎵基板上，當基溫度大於200℃時所製備的ZnSe薄膜為單晶結構。此外，我們發現低能量離子束可以清除砷化鎵基板表面的氧化層。根據拉曼光譜分析，發現在400℃成長的膜與基板間的應力為最小，且膜對488nm波長的雷射光穿透率最高。經由空間相干模型的模擬，得知350℃成長的膜其同調長度L=16.5nm為最長。對於400℃成長的膜，我們量測到其光激光光譜。在低溫(T=20K)光激光量測中，施體束縛激子(donor-bound exciton, I2)的能量為2.795 eV、半高寬為7.6meV。在變溫量測中，得到I2能量隨量測溫度變化的線性溫度係數為-4.3×10-4 eV K-1，與活化能為25 meV。|
Znse films were grown on quartzs and GaAs (100) substrates by cw CO2 laser with ion beam-assisted deposition. The films grown on quartz substrates were the zinc-blende polycrystalline structure with a strong preferred  orientation, even deposited on room teperature substrates.Without ion beam assistance, the film grown at a substrate temperature 150℃, a growth rate 6.4 A/sec had the best properties which the refractive index was 2, 5218, the extinction coefficient was 0.0016 at 700 nm and the peel strength was 11.44 mN. With ion beam assistance, the film grown at a ion beam voltage 200V, a ion beam current 15 mA was the best one whose refractive index was 2.536 close to single crystal ZnSe bulk 2.6540, extinction coefficient was 0.0010 and peel strength was 16.9 mN. From Raman measurements, the stress between the ZnSe film and the quartz substrate was 1.27×1013 dyn cm-2 We found that the properties of polycrystalline ZnSe films prepared by the system we used were better then those by the traditional thermal and electron beam evaporation. When the substrate temperature was above 200℃, the ZnSe film grown on a GaAs (100) substrate became a single crystal. By the way, we found that the low energy ion beam could remove the oxide covering over the GaAs substrate surface. Raman measurements showed that the stress between the film grown at 400℃ and the Ga As (100) substrate was smallest and the film transmittance to 488 nm laser beam was highest. According to spatial correlation model of Raman scattering, the coherence length (L=16.5 nm) of the film grown at 350℃ was longest. PL of the film grown at 400℃ was gotten. The low temperature (T=20K) PL showed that the energy of the donor-bound exciton (I2) transition was 2.795 eV and the FWHM was 7.6 meV. From PL measurements at different temperatures, the linear temperature coefficient of I2 was-4.3×10-4 eV K-1 and the activation energy was 25 meV.
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