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  • 學位論文

Si基板上III-V族化合物半導體有機金屬氣相異質磊晶研究

The study on heteroepitaxial growth of III-V compound semiconductors on Si substrate by AP-MOCVD

指導教授 : 溫武義

摘要


在本論文中,我們將描述有機金屬化學氣相沉積在矽(Si)積板上之異質磊晶成長研究。因此我們將研究的重點聚焦在砷化鎵 (GaAs)、氮化鎵 (GaN)以及氮化銦 (InN)之單晶薄膜成長。除此之外,多晶的氮化鎵 (GaN)與氮化鈦 (TiN)在本篇論文也將被探討。 首先對於GaAs成長在矽基板上,蝕刻缺陷密度低於106 cm-2之高品質GaAs磊晶層已經成功的被成長在Si (100)基板上。原子力顯微鏡觀察顯示,其GaAs磊晶層之表面粗糙度低於1.3 nm。雙晶x-ray的波峰半高寬也只有102 arcsecond。之所以能夠成長出高品質GaAs的關鍵技術,就是利用a-Si/a-GaAs雙層緩衝層再加上熱回火(in-situ thermal cyclic annealing );除此之外, KOH蝕刻技術也被成功地掌握,並且對於所顯示的結果有良好的再現性。同樣地,使用穿遂式電子顯微鏡觀測結果亦指出a-Si/a-GaAs雙層緩衝層可有效的將缺陷消除,並且讓缺陷轉向而不會傳導到GaAs表面。 緊接在後的為GaN成長在Si基板上之研究報告,為提高GaN磊晶層的品質,於磊晶生長之前,先在Si基板上進行氮化(Nitridation)處理。當Si基板在950°C溫度下利用NH3氣體處理10分鐘後, GaN磊晶層於室溫下呈現峰值3.397eV 很強的PL光譜,並且波峰半高寬為61 meV;特別是,在上述最佳化之氮化條件,其PL光譜中的黃光帶(yellow-band)可以被減弱甚至消失。另外,高解析度穿遂式電子顯微鏡顯示,經過NH3氣體處理後,矽基板表面會形成奈米罩幕,此正可有效的阻擋缺陷傳導。 對於Si基板上InN之成長研究,我們利用InN及AlN雙層緩衝層成功地將能隙0.7-0.8 eV之InN磊晶層成長在矽基板上。由布拉格繞射分析顯示此磊晶層呈現六角形的結構。另外,由霍爾量測結果知磊晶層之載子濃度與電子遷移率分別為(7-8) × 1019 cm-3與87.2 cm2/V-s。室溫下之光激螢光光譜呈現0.72 eV之峰值。改變激光功率瓦數之PL量測顯示,此InN的螢光為帶與帶(band-to-band)之間的傳輸。時間解析之PL光譜證實,其載子複合的生命週期為0.85 ns。再者,穿遂式電子顯微鏡顯示,AlN緩衝層對於六角形結構的InN成長之主導作用上扮演極重要之角色。 對於多晶之GaN薄膜,我們分別探討其發光及歐姆接觸特性,從掃描式電子顯微鏡(SEM)分析顯示,GaN的顆粒大小會隨著成長溫度改變而有所變化,另外,x-ray證實GaN為六角形結構,並且不同於GaN單晶,室溫下其PL光譜卻呈現很強的黃光帶(yellow luminescence)。隨後我們利用Ti/Au/Ni/Au多重金屬層完成了低電阻率之歐姆接觸;當回火溫度400°C且時間為120秒時,我們可以獲得多晶GaN最低的特徵接觸電阻率1.6×10-5 Ω-cm2。 最後有關Si基板上TiN 薄膜之成長,我們發現成長溫度800°C與[NH3]/[TiCl4]=0.3時,有最小的電阻率約為23.7 μΩ-cm;並且呈現金黃色的表面。原子力顯微鏡分析顯示TiN薄膜之表面粗糙度大約為5.1 nm。此外,x-ray繞射圖顯示,當成長溫度低於800°C時,其主要的x-ray主峰為TiN(200);然而,當成長溫度高達900°C時,除了TiN(200),我們可以獲得其他如TiN(111)及TiN(220) 之訊號。

並列摘要


In this thesis, the heteroepitaxial growth of III-V compound semiconductors on Si substrate by atmospheric-pressure metal-organic chemical vapor deposition (AP-MOCVD) is reported. The investigations are focused on the growth of three typical monocrystalline materials including gallium arsenide (GaAs), gallium nitride (GaN) and indium nitride (InN). Besides, the fabrication of two polycrystalline films of GaN and titanium nitride (TiN) will also be described. First for GaAs/Si, high-quality GaAs epilayers with the etch-pit density (EPD) lower than 106 cm-2 have been grown on Si (100) substrate. The Atomic Force Microscopy (AFM) images exhibited that the root-mean-square (RMS) value of the surface morphology was only 1.331 nm. The full width at half maximum (FWHM) of the double crystal X-ray rocking curve in the (400) reflection was about 102 arcsec. A key technology of the use of a-GaAs/a-Si double buffers accompanied by in-situ thermal cyclic annealing treatment was developed to achieve this result. Besides, a well-controlled molten KOH etching technique was established to evaluate the EPD of GaAs epilayer with good reproducibility. Also, the effect of a-GaAs/a-Si double buffers was examined in detail by transmission electron microscopy (TEM). Next, for GaN/Si high quality single crystalline GaN layers were grown on Si (111) substrates by using a silicon nitride (SiNx) buffer achieved through the nitridation of substrate. A strong photoluminescence (PL) emission at 365 nm (3.4 eV) with the FWHM of 61.1 meV was achieved at room temperature when the substrate was nitrided at 950°C for 10 min. Particularly, it was found that a yellow luminescent band disappeared when nitridation was performed at temperatures higher than 950°C. The masking effect of porous SiNx buffer was recognized by TEM observation, which is considered to block the threading dislocations and resulted in goo-quality GaN epilayers. For InN/Si, InN epilayers with the band-gap energy between 0.7 – 0.8 eV have been successfully grown on Si (111) substrates with low-temperature (450aC) grown InN and high-temperature (1050ºC) grown AlN (InN/AlN) double-buffer layers. X-ray diffraction (XRD) characterizations indicated that highly (0001)-oriented hexagonal InN was grown on Si (111) substrate. Hall measurements showed the mobility and carrier concentration were 87.2 cm2/V-s and (7-8) × 1019 cm-3, respectively. PL analyses performed at room temperature showed a strong emission at 0.72 eV with a full-width at half-maximum of 121 meV. Excitation intensity dependent measurements demonstrated the PL mechanism to be the band-to-band transition. Time-resolved PL could be fitted by a single exponential exhibiting an ordered film and a recombination lifetime of around 0.85 ns. In particular, TEM characterizations indicated that the use of AlN first buffer is effective to obtain an InN epilayer with hexagonal structure. As an option to use GaN, poly-crystalline GaN films were also grown and their optical properties and ohmic contact characteristics were examined. Scanning electron microscopy analyses display that the shape and size of GaN grains are quite dependent on the growth temperature. XRD characterizations show that the polycrystalline GaN exhibits wurtzite structure with a preferential (0001) orientation. PL spectra show a strong yellow luminescence from the poly-GaN films. Furthermore, a low-resistivity ohmic contact to poly-GaN was achieved using the multilayer metal combination of Ti (50Å)/Au (100Å)/Ni (100Å)/Au (3000Å). An improvement in 歊 of over one order of magnitude was achieved over the as-deposited condition with good reproducibility by RTA treatment for a total duration of 120 s. In particular, by optimizing the annealing temperature to 400°C a relatively low 歊 of 1.6×10-5 Ω-cm2 was yielded for the contact of Ti/Au/Ni/Au to poly-GaN with a carrier concentration of (5-6)×1017 cm-3. Finally, for TiN/Si, the TiN films were obtained by exploiting TiCl4+NH3 gas chemistry with flow ratios from [NH3]/[TiCl4]=0.2 to 1.4, and deposition temperatures (Td) from 600 to 900°C. When Td = 800°C gold-colored films with electrical resistivities of under 100 μΩ cm were formed at almost all of the investigated flow ratios. In particular, a lowest resistivity of about 23.7 μΩ cm, which is quite close to that of bulk TiN, was achieved using an flow ratio of 0.3. AFM characterizations indicated that the root mean square surface roughness of that film was only about 5.1 nm. Under the same [NH3]/[TiCl4] flow ratio as above, XRD analyses revealed the presence of a cubic TiN phase with a preferred orientation of (200) for Td < 800°C, while additional (111) and (220) orientations emerged when the film was deposited at 900aC. In conclusion, a low resistivity (<100 μΩ cm) TiN film can be formed on Si substrate with very low flow ratios [NH3]/[TiCl4]=0.3 – 1.4.

並列關鍵字

GaAs TEM InN III-V compound semiconductor GaN Si substrate

參考文獻


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