GaN载流子浓度和迁移率的光谱研究

用红外反射光谱的方法对生长在蓝宝石衬底上的α-GaN外延薄膜的载流子浓度和迁移率进行了研究.通过测量蓝宝石衬底和不同Si掺杂浓度的一系列GaN外延膜的远红外反射谱并进行理论计算和拟合,得到GaN中的声子振动参量和等离子振荡的频率及阻尼常量,并由此计算得到其载流子浓度和迁移率.计算结果,红外方法得到的载流子浓度与Hall测量相一致,但迁移率比Hall迁移率要低约二分之一.同时红外谱与喇曼谱上明显观察到LO声子与等离子体激元耦合模,(LPP)随掺杂浓度的变化. 关键词： α-GaN外延薄膜 红外反射光谱 载流子浓度 迁移率 LO声子与等离子体激元耦合模 Raman光谱     

半导体氮化铟(InN)的晶格振动

本文总结了新型半导体InN薄膜晶格振动研究的现状,主要为Raman散射光谱及部分红外光谱的研究结果。重点内容为InN(包括六方纤锌矿结构和立方闪锌矿结构)的布里渊区中心(Γ点)声子结构、电子激发态(等离子激元)与纵光学声子耦合、无序化激发模和晶格振动模的温度、应力效应等,也涉及部分和InN有关的氮化物合金以及超晶格、量子阱和量子点等结构的晶格振动研究。同时对相关材料和结构的Raman光谱研究作了一些展望。     

半导体氮化铟(InN)的晶格振动

本文总结了新型半导体InN薄膜晶格振动研究的现状，主要为Raman散射光谱及部分红外光谱的研究结果。重点内容为InN(包括六方纤锌矿结构和立方闪锌矿结构)的布里渊区中心(Γ点)声子结构、电子激发态(等离子激元)与纵光学声子耦合、无序化激发模和晶格振动模的温度、应力效应等，也涉及部分和InN有关的氮化物合金以及超晶格、量子阱和量子点等结构的晶格振动研究。同时对相关材料和结构的Raman光谱研究作了一些展望。     

重碳掺杂p型GaAs中纵光学声子与等离振子耦合模的Raman散射特性

对用MOMBE法生长的重C掺杂p型GaAs进行了Raman散射研究,结合理论分析,较好地解释了p型GaAs中纵光学(LO)声子与空穴等离振子耦合(LOPC)模的Raman散射特性,证明它具有与n型状态不同的特点,根据实验结果讨论了重掺杂对Raman散射谱的影响,发现LOPC模的散射峰特征(位置和宽度)与重掺杂效应程度具有很大关系。     

GaMnAs合金中等离子体激元-LO声子耦合模的拉曼光谱研究

理论分析了两种阻尼条件下重掺杂GaAs中的等离子体激元-LO声子耦合模,证实在小阻尼条件下耦合模的拉曼谱分为两支,而在大阻尼条件下只有一个耦合模可以被观测到。推导得到了只出现一个耦合模所需的最小阻尼的解析表达式。测量了Mn组分从2.6%到9%的GaMnAs合金的拉曼光谱。利用等离子体激元-LO声子耦合模理论进行了谱形拟合,得到了所测的GaMnAs合金中的空穴浓度。     

掺Ni的ZnO粉末的Raman光谱研究

利用拉曼(Raman)光谱对掺镍(Ni)氧化锌(ZnO)粉末的声子谱进行了研究.在掺杂样品的Raman光谱中仍能观察到未掺杂ZnO的声子模式,此外还观察到两个额外模式.掺杂粉末中观察到ZnO的E2(h)模式表明掺Ni的ZnO仍然保持六角对称结构.652 cm-1额外模式的起源是掺杂引起的ZnO本底缺陷.为了查明544 cm-1处额外模式的起源,分别对掺Ni,掺钴(Co),和掺锰(Mn)的ZnO粉末的Raman光谱进行了对比研究.结果表明544 cm-1额外模式起源于Ni相关的局域振动模式.对光谱中的其他声子模式的起源也进行了讨论;同时还报告了利用325nm激光作激发源观察到掺Ni样品的多重纵光学(LO)声子模式的结果.     

P-MBE制备氮掺杂p型ZnO中空穴的散射机制

利用等离子体辅助的分子束外延(P-MBE)技术,在蓝宝石衬底上制备了氮掺杂的p型ZnO薄膜。通过变温霍尔测量研究了空穴浓度和迁移率随温度的变化特性。对载流子浓度拟合的结果表明氮受主具有75meV的能级深度。通过对各种散射机制下迁移率的讨论,发现由晶粒及其晶界组成的这种结构极大地降低了p型ZnO中载流子的迁移率。     

离子注入法制备GaN∶Er薄膜的Raman光谱分析

对离子注入法制备的u-,n-和p-GaN∶Er三种类型的薄膜样品进行了Raman光谱分析。Er+注入GaN样品后新出现了293,362和670 cm-1等波数的Raman峰,其中293 cm-1处的Raman峰被指认为无序激活的Raman散射(DARS),362 cm-1和670 cm-1处的Raman峰可能与离子注入后形成的GaN晶格缺陷有关。上述GaN∶Er样品在800℃退火前后的E₂(high)特征峰均向高频方向移动,表明薄膜晶格中均存在着压应力。采用洛伦兹拟合分析了Raman光谱中组成A₁(LO)模式峰的未耦合LO模与等离子体激元耦合模LPP+在不同样品中的出现情况,定性指出了GaN∶Er系列样品中载流子浓度的变化规律。     

在不同衬底温度下用直流反应磁控溅射法制备p型ZnO薄膜

采用直流反应磁控溅射方法,通过改变衬底温度并优化生长参数,在玻璃衬底上生长了In-N共掺p型ZnO薄膜。X射线衍射(XRD)测试表明,所得薄膜结晶性能良好,且具有很好的c轴择优取向。Hall测试的结果所得p型ZnO薄膜最低电阻率为35.6Ω·cm,霍尔迁移率为0.111cm2·V-1·s-1,空穴浓度为1.57×1018cm-3。X光电子能谱(XPS)测试表明,铟元素已有效地掺入了ZnO薄膜中,且铟元素有效地促进了氮元素的掺入。紫外可见(UV)透射谱测试表明,在可见光范围内所有薄膜透光率均可达90%。     

铋纳米薄膜相干光学声子研究

利用共轴双色飞秒激光泵浦-探测技术测量了铋(Bi)纳米薄膜的相干光学声子。采用自相关技术测量得到探测光的脉宽约为45 fs,用探测光和泵浦光的互相关信号得到泵浦光经过脉冲整形以后的脉宽约为250 fs,进而测量得到Bi纳米薄膜的对称振动模频率为2.86 THz,与自发Raman光谱的结果吻合。采用指数衰减函数与互相关信号的卷积拟合延迟时间在10 ps以内的差分反射信号,确定了相干光学声子振幅衰减的特征时间约为2.6 ps,与电子衰减特征时间相近,却远小于晶格加热的特征时间,从而为进一步揭示材料内部载流子与声子的相互作用提供了依据。     

N离子注入富氧ZnO薄膜的p型导电及拉曼特性研究

采用射频磁控溅射法在富氧环境下制备ZnO薄膜, 继而结合N离子注入及热退火实现薄膜的N掺杂及p 型转变, 借助霍尔测试和拉曼光谱研究了N离子注入富氧ZnO薄膜的p型导电及拉曼特性. 结果表明, 在 600 ℃温度下退火120 min可获得性能较优的p-ZnO: N薄膜, 其空穴浓度约为2.527×10¹⁷ cm^-3. N离子注入ZnO引入了三个附加拉曼振动模, 分别位于274.2, 506.7和640.4 cm^-1. 结合电学及拉曼光谱的分析发现, 退火过程中施主缺陷与N受主之间的相互作用对p-ZnO的形成产生重要影响.     

Fabrication of high hole-carrier density p-type ZnO thin films by N-Al co-doping

In order to obtain p-type ZnO thin films, effect of atomic ratio of Zn:N:Al on the electronic and structural characteristic of ZnO thin films was investigated. Hall measurement indicated that with the increase of Al doping, conductive type of as-grown ZnO thin films changed from n-type to p-type and then to n-type again, reasons are discussed in details. Results of X-ray diffraction revealed that co-doped ZnO thin films have similar crystallization characteristic (0 0 2 preferential orientation) like that of un-doping. However, SEM measurement indicated that co-doped ZnO thin films have different surface morphology compared with un-doped ZnO thin films. p-type ZnO thin films with high hole concentration were obtained on glass (4.6 × 10¹⁸ cm⁻³) and n-type silicon (7.51 × 10¹⁹ cm⁻³), respectively.     

p-Type conduction in phosphorus-doped ZnO thin films by MOCVD and thermal activation of the dopant

Phosphorus-doped p-type ZnO thin films have been realized by metalorganic chemical vapor deposition (MOCVD). The conduction type of ZnO films is greatly dependent on the growth temperature. ZnO films have the lowest resistivity of 11.3 Ωcm and the highest hole concentration of 8.84 × 10¹⁸ cm⁻³ at 420 °C. When the growth temperature is higher than 440 °C, p-type ZnO films cannot be achieved. All the films exhibited p-type conduction after annealing, and the electrical properties were improved comparing with the as-grown samples. Secondary ion mass spectroscopy (SIMS) test proved that phosphorus (P) has been incorporated into ZnO.     

Preparation of p-type ZnO:(Al, N) by a combination of sol--gel and ion-implantation techniques

We report the preparation of p-type ZnO thin films on (0001) sapphire substrates by a combination of sol--gel and ion-implantation techniques. The results of the Hall-effect measurements carried out at room temperature indicate that the N-implanted ZnO:Al films annealed at 600\du\ have converted to p-type conduction with a hole concentration of $1.6\times10¹⁸cm^-3, a hole mobility of 3.67cm²/V.s and a minimum resistivity of 4.80cm.\Omega$. Ion-beam induced damage recovery has been investigated by x-ray diffraction (XRD), photoluminescence (PL) and optical transmittance measurements. Results show that diffraction peaks and PL intensities are decreased by N ion implantation, but they nearly recover after annealing at 600\du. Our results demonstrate a promising approach to fabricate p-type ZnO at a low cost.     

Induction of p-type conduction in sputtered deposited Al-N codoped ZnO thin films

Al and N codoped ZnO thin films were grown on n-Si (100) substrate by sputtering technique. Hall effect measurements of as-grown films exhibited n-type conduction, however 500 °C Ar annealed codoped films showed p-type conductivity with a hole concentration of 9.9 × 10¹⁶ cm^− 3, resistivity of 15.95 Ω-cm and hole mobility of 3.95 cm²/Vs, respectively. Codoped ZnO thin films were found to be highly c-axis oriented with good crystal quality. A neutral acceptor-bound exciton and donor-acceptor-pair emissions that appeared at room temperature photoluminescence measurement verify p-type conduction in Al and N codoped ZnO film. The current-voltage characteristics of p-n heterojunction evidently showed a diode like rectifying behaviour.     

Effects of annealing ambience on ZnO:N films grown by MOCVD and the p-type doping mechanism of ZnO:N films investigated by XANES

ZnO:N thin films were deposited on sapphire substrate by metal organic chemical vapor deposition with NH₃ as N-doping sources. The reproducible p-type ZnO:N film with hole concentration of ∼10¹⁷ cm⁻³ was successfully achieved by subsequent in situ thermal annealing in N₂O plasma protective ambient, while only weak p-type ZnO:N film with remarkably lower hole concentration of ∼10¹⁵ cm⁻³ was obtained by annealing in O₂ ambient. To understand the mechanism of the p-type doping behavior of ZnO:N film, X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption near-edge spectroscopy (XANES) measurements have been applied to investigate the local electronic structure and chemical states of nitrogen atoms in ZnO:N films.     

硼对氮掺杂的p型ZnO薄膜的影响

利用分子束外延设备在蓝宝石衬底上生长了B/N共掺的p型ZnO薄膜,对比了B/N共掺和N单掺杂样品的物理学性能。通过X射线光电子能谱测试证明了在薄膜中存在有B和B-N键。B/N共掺样品的空穴浓度比单一N掺杂样品高近两个量级。且ZnO：（B,N）薄膜在两年多的时间内一直显示稳定的p型电导。这是由于B-N键的存在提高了N在ZnO薄膜中的固溶度,且B-N键之间强的键能和B占据Zn位所表现的弱施主特性不会带来强的施主补偿效应,说明B是N掺杂ZnO薄膜的一种良好的共掺元素。     

Characterization and aging effect study of nitrogen-doped ZnO nanofilm

The influence of sputtering and annealing conditions and aging effect on properties of sputtered ZnO:N thin films were investigated. Achieved results confirmed a planar growth of nitrogen-doped ZnO film with a high uniform and smooth surface morphology. Incorporation of nitrogen in the ZnO films made new Raman shifts. X-ray diffraction spectra showed only the ZnO (0 0 2) diffraction peak, which was slightly shifted toward lower angels, compared to pure ZnO, which is the result of incorporating nitrogen in the ZnO films. The amount of this shift was proportional to N concentration. In addition, annealed samples showed better crystallinity with lower shift due to dramatically reduction of N atoms during the annealing. The Hall effect measurements exhibited p-type behaviour on annealed ZnO:N thin films while the un-annealed samples showed n-type conductivity. Aging effect studies demonstrated that the N content of thin films decreased dramatically as time passed. The reduction of N concentration in annealed samples was lower than un-annealed ones after 6 months.     

Fabrication and characterization of magnetron sputtered arsenic doped p-type ZnO epitaxial thin films

Arsenic doped p-type ZnO thin films were grown on sapphire substrate by magnetron sputtering. As grown films reveal p-type conduction confirmed by Hall-effect and photoluminescence measurements. The p-type film with a hole concentration of 2.16× 10¹⁷ cm⁻³, mobility of 1.30 cm²/V.s and resistivity of 22.29 Ω-m were obtained at substrate temperature of 700 °C. ZnO homojunction synthesized by in-situ deposition of As doped p-ZnO layer on Al doped n-ZnO layer showed p-n diode like characteristics. X-ray pole figure and Transmission Electron Microscope studies confirm epitaxial nature of the films. Photoluminescence results exhibit the peaks associated with donor acceptor pair emission.     

Fabrication of Sb-doped p-type ZnO thin films by pulsed laser deposition

p-Type ZnO thin films have been realized via monodoping antimony (Sb) acceptor by using pulsed laser deposition. The obtained films with the best electrical properties show a hole concentration in the order of 10¹⁸ cm⁻³ and resistivity in the range of 2-4 Ω cm. X-ray diffraction measurements revealed that all the films possessed a good crystallinity with (0 0 2)-preferred orientation. Guided by X-ray photoemission spectroscopy analysis and a model for large-sized-mismatched group-V dopant in ZnO, an Sb_Zn-2V_Zn complex is believed to be the most possible acceptor in the Sb-doped p-type ZnO thin films.