MOCVD生长GaN膜的光调制反射谱研究

采用光调制反射光谱（PR）研究了（0001）晶向蓝宝石村底上MOCVD方法生长的单晶六角GaN薄膜的室温光学性质。测得六角GaN薄膜的禁带宽度为3．400eV，对PR谱的调制机理进行了分析，发现信号来自缺陷作用下的表面电场调制。光吸收增和光反射谱的测量，得到3．39eV的光学吸收边和3．3eV的反射峰，证实了光调制反射光谱的结果。     

Photoreflectance study of δ-doped semiconductor layers by a fast Fourier transformation

Photoreflectance (PR) spectroscopy has been applied to the investigation of Si δ-doped GaAs, Al_0.35Ga_0.65As and AlAs layers grown by metal–organic vapor phase epitaxy (MOVPE) on GaAs substrates. The observation of Franz–Keldysh oscillations (FKO) and the application of fast Fourier transform (FFT) has allowed us to determine the internal electric field and, hence, the potential barrier between surface and δ-doped region of the layer. The FFT of the photoreflectance spectra has exhibited two separate heavy and light hole frequencies showing that the FKO in the PR signal are always the superposition of these two components.     

Annealing study of InGaP/GaAs heterojunction bipolar transistor and carbon-doped pGaAs base layers

In this work we have examined the effect of RF annealing (450–750°C, 5–30 min) upon both InGaP/GaAs-based hetero-junction bipolar transistor (HBT) structures, fabricated by metalorganic vapour phase epitaxy (MOVPE), as well as thick carbon (C)-doped p⁺GaAs HBT base layers with varying layer thickness, dopant level and type (intrinsic and extrinsic C precursors) and co-doping (In) strain compensation. Anneal-induced changes in the p⁺GaAs layer lattice strain, Hall carrier concentration and mobility were compared with non-radiative losses, determined from photoluminescence (PL) intensity data. Majority and minority carrier property differences were also compared with IR reflection, Raman backscattering and photoreflectance (PR) data and correlated with changes in MOVPE hydrogen background concentration as determined by secondary-ion-mass-spectroscopy (SIMS). Thick base layer (1.3 μm) HBT structures were also examined for different anneal temperatures and time, showing significant changes in the PR emitter(InGaP)/base (p⁺GaAs) and base/collector (n-GaAs) interface regions for the 650°C anneal condition, as correlated with both PL and SIMS hydrogen concentration data.     

异质结NIPI结构的光调制反射光谱

本文首次报道了异质结NIPI结构的室温光调制反射光谱及其随调制光强的变化,并对调制机制进行了讨论.最后,通过比较理论与实验结果,对所观测到的跃迁过程进行了指派.     

从势垒区电压波形对照GaAs液结的光调制反射与电调制反射

通过直接观察n型GaAs-电解液结表面势垒的电压,对光反射和电反射的内在规律进行了比较.引入一个新的参数,来精细地区别这两种调制.从脉冲激光或(和)外加调制电压下空间电荷区中电场的具体分布,解释了二种调制光谱的共同点和差别.     

Three beam photoreflectance as a powerful method to investigate semiconductor heterostructures

We have proposed three beam photoreflectance (TBPR) technique as a powerful tool to investigate the nature of PR resonances associated with transitions in quantum wells (QWs) placed in a weak surface electric field. This method works as a contactless forward bias and allows changing the internal fields even down to the flat band conditions. We have shown that changes in built-in electric field by amount of a few tenths of kV/cm can modify the transition intensities significantly whereas the transition energies are being kept unchanged and no Stark shift of the QW energy levels is detected. The intensity changes make it possible to distinguish between the parity allowed and forbidden optical transitions in a quantum well.     

Bandgap modifications by lattice deformations in β-FeSi2 epitaxial films

The modifications of direct transition energies by lattice deformations were investigated in β-FeSi₂ epitaxial films, polycrystal films and single crystal, systematically. The lattice deformations depending on thermal annealing temperature (T_a) were observed in β-FeSi₂ epitaxial films. In photoreflectance (PR) measurements, the direct transition energies of the epitaxial films shifted to lower energies as the T_a increased. The polycrystal films did not show the lattice deformation and the shift of direct transition energies. These results show that the direct bandgap is modified by the lattice deformation originating from the lattice mismatch at the hetero-interface of β-FeSi₂/Si.