Transport and optical properties of Al2O3/Ga2O3(Gd2O3)/In0.2Ga0.8As/GaAs multilayer structure

氧化鋁/氧化鎵(氧化釓)/砷化銦鎵/砷化鎵多層結構之傳輸性質及光學性質

莊卓穎(Cho-Ying Chuang)

指導教授 ： 郭瑞年 ； 洪銘輝

國立清華大學/理學院/物理學系/碩士(2009年)

https://doi.org/10.6843/NTHU.2009.00474

摘要

In the microelectronics industry, the scaling trends of SiO2/Si have encountered great difficulties due to the effect of quantum tunneling. The integration of high-mobility channels of III-V (or Ge) with high-k dielectric materials is regarded as a promising approach to replace SiO2/Si. As a result, knowledge related to the basic electronic properties of these materials, such as trap states, is essential. In this study, the interface properties of MBE-grown Al2O3/Ga2O3(Gd2O3)[GGO]/n-In0.2Ga0.8As/n-GaAs heterostructure have been investigated by transport and optical approaches.
Our study started with the transport properties of Al/Al2O3/GGO /In0.2Ga0.8As/GaAs. After 850oC rapid thermal annealing (RTA), the  value of GGO remained around 12-15 and well-behaved capacitance-voltage (C-V) curves with very low frequency dispersion in accumulation (1.4%-4.7%) were observed. The leakage current densities were about 10-9 A/cm2 at Vfb+1V. A noteworthy result is that the scaling of the high-k oxides to about 1.0 nm capacitance equivalent thickness (CET) was achieved in a GGO/In0.2Ga0.8As gate stack. In addition, remarkable Fermi-level movement efficiency (FLME) to about 80% was obtained as determined by the quasi-static capacitance-voltage (QS-CV) measurement. The observation demonstrates that high-k dielectric GGO on InGaAs has successfully unpinned the Fermi level.
On the other hand, we proposed a novel optical technique called Time-Resolved Second-Harmonic Generation (TRSHG) to explore the interfacial quality of oxide/semiconductor. Optical second-harmonic generation (SHG) is a noninvasive optical probe to investigate electronic structure and chemical dynamics at sample surfaces. However, after carefully analyzing the coherent phonon spectra, no information from oxide/semiconductor interface can be directly obtained because of the strong interaction of LO phonon-plasmon coupling mode in InGaAs/GaAs polar semiconductor. Nevertheless, one finding is that the defects in InGaAs strain layer increased after RTA. This observation was also proved by TRSHG phonon strength and Raman intensity.
In conclusion, the transport properties of the novel Al2O3/GGO/In0.2Ga0.8As/GaAs heterostructure significantly improved after RTA, and Fermi-level was demonstrated to move almost freely in the bandgap of III-V based MOS capacitors. Combining the electrical and optical measurements, the observation indicated that the improvement in transport properties made by RTA, which repaired the oxide layer, is greater than the damage to InGaAs substrate due to its thermal effect. Although the optical results in this study cannot reveal the direct information of oxide/polar-semiconductor interface, it is still possible to acquire the interfacial information by using optical SHG technique with non-polar semiconductor (Si or Ge) as the substrate.

關鍵字

分子束磊晶 ； 高介電係數閘極氧化層 ； 三五族化合物半導體 ； 氧化鎵(氧化釓) ； 砷化銦鎵 ； 介面缺陷密度 ； 時間解析二倍頻 ； 同調聲子光譜 ； 聲子-電漿子耦合交互作用

並列摘要

隨著尺寸的微小化，二氧化矽/矽的半導體元件已逐漸逼近其量子穿隧極限，因此，高介電係數的閘極氧化層及高電子遷移率的基板(三五族半導體及鍺)即成為取代二氧化矽/矽系統的最佳候選人。然而，如何定義高介電閘極氧化層與半導體間的介面特性仍是個重大課題。本實驗結合傳輸與光學方法，探討分子束磊晶成長的氧化鋁/氧化鎵(氧化釓)/砷化銦鎵/砷化鎵之介面性質。
傳輸性質方面，不同氧化鎵(氧化釓)厚度條件(20, 10, 7, 3.6 nm)，經過氫氣下的850oC快速高溫熱退火，此異質結構呈現極佳的電性。電容-電壓量測結果顯示，介電常數均維持在12-15、10到500千赫茲間的積聚電容值頻率分散皆在5%以下，且最小等效電容厚度(Capacitive effective thickness, CET)可達1 nm。電流-電壓量測結果顯示，平帶電壓加1V處之漏電流密度低至10-9A/cm2。而在擬穩態電容-電壓量測下，電容-電壓曲線中的少數載子反轉行為與理想曲線的吻合度達80%，顯示氧化鎵(氧化釓)可有效鈍化砷化銦鎵表面，讓費米能階在外加電壓下可近乎自由活動。
光學性質方面，我們使用新穎的時間解析二倍頻技術來探討介面性質。二倍頻的優點在於不只量到表面訊號，還可量測到埋在下層的介面訊號。但分析實驗所得的同調聲子光譜後發現，由於砷化銦鎵/砷化鎵基板為極性半導體，有較複雜的聲子-電漿子耦合交互作用，以至於我們無法直接得到微弱的氧化物/半導體介面訊號。不過我們也意外發現砷化銦鎵在850oC快速高溫熱退火後，出現較多晶格缺陷的實驗證據，此現象同時也在拉曼光譜上證實。
在這個研究中，此異質結構呈現極佳的傳輸性質，且我們發現快速高溫熱退火對氧化層修復的功效遠大於對砷化銦鎵的負面影響。雖然我們沒有成功的用光學方法看到氧化物/半導體介面訊號，但若適當的修正實驗，例如使用非極性的矽或鍺基板，二倍頻技術仍有機會得到氧化物/半導體介面資訊。了解其傳輸性質及光學性質將有助於我們判斷高介電閘極氧化層與半導體間的介面特性。

並列關鍵字

molecular beam epitaxy ； high-k gate dielectric ； III-V semiconductor ； Ga2O3(Gd2O3) ； InGaAs ； interface trap ； time-resolved second-harmonic generation ； coherent phonon spectrum ； phonon-plasmon coupling

參考文獻

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