Atomic Layer Deposited p-type Oxide Semiconductor Thin Films : Fundamental, Process and Thin Film Transistor

Abstract

In recent years, oxide semiconductor materials attracted its attention for gas sensors, solar cells, photocatalysis, transparent electrodes, and thin film transistors (TFTs). However, most of oxide semiconductor materials were n-type materials. The n-type materials such as such indium-gallium-zinc oxide (IGZO) has spherical symmetry of the s orbitals of the metal cation, which are widely overlap each other, and allow the electrons to be delocalized. The delocalized electrons could be a pathway for electron transfer, enable to achieve high mobility. On the other hand, in the p-type oxide semiconductors, valence band (VB) act as a hole conduction pathway. The VB is mainly consisted with the anisotropic and localized oxygen 2p orbitals, resulting in poor hole mobility. Also, high formation energy of metal vacancy site induced low carrier concentration. Owing to those disadvantages, fabricating high performance p-type oxide semiconductor materials is challenging. SnO has been arising as a promising p-type material due to its low formation energy of Sn2+ vacancy site (VSn), which inducing high carrier concentration and delocalized VB comes from hybridization of oxygen 2p orbitals and tin 5s orbitals.

However, the Sn cation could exist with oxidation states of Sn2+and Sn4+, as a result, tin oxide can be found in two phases: tin dioxide (SnO2) and tin monoxide (SnO). SnO2 and SnO thin films have difference chemical, physical, and electrical properties. SnO2 is an n-type semiconductor material with a high hall mobility, high electron carrier concentration, and low resistivity. On the other hand, SnO is a p-type semiconductor material owing to substantial quantities of native acceptors. Here, in this thesis, divalent Sn precursor was used, N,N’-tert-butyl-1,1-dimethylethylenediamine stannylene (II), to deposit SnOx thin films by atomic layer deposition (ALD). The two types of SnO and SnO2, were selectively fabricated by using different reactants. Ozone and water preferentially generated SnO2 and SnO films, respectively. Density functional theory (DFT) calculations have showed the oxidative power of ozone and water, and their chemical affinity to the preformed SnO2 and SnO films determine the growth phenomenon of SnOx films. Also, applying post annealing process, we could optimize the electrical properties of SnO thin films and successfully fabricated TFTs using SnO. In conclusion, SnO with p-type semiconductor property film was successfully demonstrated using ALD method. Furthermore, NiO was deposited using Ni(dmamb)2 precursor and shows p-type property by optimizing defect in deposited thin films. As a result, SnO and NiO might be promising materials for p-type oxide semiconductor material.

|최근, 산화물 반도체 재료는 가스 센서, 태양 전지, 광촉매, 투명 전극 및 박막 트랜지스터 (TFT)에 다양하게 사용되었다. 그러나, 현재까지의 산화물 반도체 재료의 대부분은 n-형 재료이다. 인듐-갈륨-아연 산화물 (IGZO)과 같은 n-형 물질은, 구면 대칭을 가지는 금속 양이온의 s 궤도가 서로 겹치며 전자가 비 편재화 될 수 있게 한다. 이렇게 비 편재화 된 전자는 전자 이동을 위한 경로로 작용하며 n-형 반도체가 높은 이동성을 달성할 수 있게 작용한다. 한편, p 형 산화물 반도체에서, 가전 자대 (VB)는 정공 전도 경로로써 작용한다. 이러한 가전자대는 주로 이방성이 있고 국지화 되어 있는 2p 궤도로 구성되어 정공 이동이 제한되며 정공 이동성이 좋지 않습니다. 또한, 금속 공공의 높은 형성 에너지는 p-형 반도체 내부에서 낮은 캐리어 농도를 유도하게 된다. 이러한 단점으로 인해, 고성능 p-형 산화물 반도체 재료를 제조하는 것은 어렵다. 이중 SnO는 Sn2+ 공공의 (VSn)의 낮은 형성 에너지와 산소 2p 궤도 및 주석 5s 궤도의 혼성화에서 비롯되는 비편재화된 가전자대로 인하여 유망한 p-형 물질로 각광받고 있다. 하지만, Sn 양이온은 Sn2+ 및 Sn4+의 산화 상태로 존재할 수 있으며, 그 결과, 이산화 주석 (SnO2) 및 일산화 주석 (SnO)의 두 상으로 발견된다.

SnO2와 SnO 박막은 화학적, 물리적, 전기적 특성에 차이가 있다. SnO2는 높은 홀 이동도, 높은 전자 캐리어 농도 및 낮은 저항을 갖는 n- 형 반도체 재료이다. 한편, SnO는 상당한 정공 생성 결함으로 인해 p-형 반도체 물질이다. 여기서, 본 논문에서는 원자 층 증착 (ALD)에 의해 SnOx 박막을 증착 시키기 위해 2가 Sn 전구체 인 N, N’-tert-butyl-1,1-dimethylethylenediamine stannylene (II)을 사용하였으며. SnO 및 SnO2는 상이한 반응물을 사용하여 선택적으로 제조되었다. 범 밀도함수 계산은 SnO2와 SnO 필름에 대한 오존과 물의 화학적 친화력이 SnOx 필름의 성장을 결정한다는 점을 알 수 있었습니다. 또한, 후 열처리 공정을 적용하여, SnO 박막의 전기적 특성과 TFT를 성공적으로 제조할 수 있었습니다. 결론적으로, p 형 반도체 특성 막을 갖는 SnO는 ALD 법을 사용하여 성공적으로 입증되었으며, 이는 p 형 산화물 반도체 재료를 위한 유망한 재료 일 수 있다 생각되어 집니다. 또 다른 예로서 Ni(bis(1-dimethylamino-2-methyl-2-butanolate), Ni(dmamb)2 를 이용하여 NiO 박막을 증착 하였으며, NiO 박막내의 결함 제어를 통하여 p-type 특성의 발현이 가능한 점을 알 수 있었다. 이는 SnO와 NiO가 p-형 산화물 반도체 재료로써 유망한 재료 일 수 있다 생각되어 진다.; In recent years, oxide semiconductor materials attracted its attention for gas sensors, solar cells, photocatalysis, transparent electrodes, and thin film transistors (TFTs). However, most of oxide semiconductor materials were n-type materials. The n-type materials such as such indium-gallium-zinc oxide (IGZO) has spherical symmetry of the s orbitals of the metal cation, which are widely overlap each other, and allow the electrons to be delocalized. The delocalized electrons could be a pathway for electron transfer, enable to achieve high mobility. On the other hand, in the p-type oxide semiconductors, valence band (VB) act as a hole conduction pathway. The VB is mainly consisted with the anisotropic and localized oxygen 2p orbitals, resulting in poor hole mobility. Also, high formation energy of metal vacancy site induced low carrier concentration. Owing to those disadvantages, fabricating high performance p-type oxide semiconductor materials is challenging. SnO has been arising as a promising p-type material due to its low formation energy of Sn2+ vacancy site (VSn), which inducing high carrier concentration and delocalized VB comes from hybridization of oxygen 2p orbitals and tin 5s orbitals.

However, the Sn cation could exist with oxidation states of Sn2+and Sn4+, as a result, tin oxide can be found in two phases: tin dioxide (SnO2) and tin monoxide (SnO). SnO2 and SnO thin films have difference chemical, physical, and electrical properties. SnO2 is an n-type semiconductor material with a high hall mobility, high electron carrier concentration, and low resistivity. On the other hand, SnO is a p-type semiconductor material owing to substantial quantities of native acceptors. Here, in this thesis, divalent Sn precursor was used, N,N’-tert-butyl-1,1-dimethylethylenediamine stannylene (II), to deposit SnOx thin films by atomic layer deposition (ALD). The two types of SnO and SnO2, were selectively fabricated by using different reactants. Ozone and water preferentially generated SnO2 and SnO films, respectively. Density functional theory (DFT) calculations have showed the oxidative power of ozone and water, and their chemical affinity to the preformed SnO2 and SnO films determine the growth phenomenon of SnOx films. Also, applying post annealing process, we could optimize the electrical properties of SnO thin films and successfully fabricated TFTs using SnO. In conclusion, SnO with p-type semiconductor property film was successfully demonstrated using ALD method. Furthermore, NiO was deposited using Ni(dmamb)2 precursor and shows p-type property by optimizing defect in deposited thin films. As a result, SnO and NiO might be promising materials for p-type oxide semiconductor material.