脉冲强激光破坏Hg0.8Cd0.2Te晶片材料的机理分析

利用光学金相显微镜对TEA-CO2脉冲强激光辐照的Hg0.8Cd0.2Te晶片表面进行了观察。在单脉冲能量为37.5 J,能量密度为937.5 J/cm2的强激光辐照下,晶片表面呈现出熔融迹象和大量的微裂纹,微裂纹密度从激光辐照区中心向外逐渐减少,裂纹沿晶体的(111)面扩展。随着脉冲连续作用次数的增加,晶片表面熔融更加剧烈,裂纹数目、裂纹深度和宽度都有所增加。分析认为：HgCdTe晶片的破坏与激光辐照能量、脉冲连续作用次数、激光场强分布、激光热应力、激光支持的燃烧波和物质的蒸发波等冲击波有关。     

脉冲强激光破坏Hg0.8Cd0.2Te晶片材料的机理分析

 利用光学金相显微镜对TEA-CO₂脉冲强激光辐照的Hg_0.8Cd_0.2Te晶片表面进行了观察。在单脉冲能量为37.5 J，能量密度为937.5 J/cm²的强激光辐照下，晶片表面呈现出熔融迹象和大量的微裂纹，微裂纹密度从激光辐照区中心向外逐渐减少，裂纹沿晶体的(111)面扩展。随着脉冲连续作用次数的增加，晶片表面熔融更加剧烈，裂纹数目、裂纹深度和宽度都有所增加。分析认为：HgCdTe晶片的破坏与激光辐照能量、脉冲连续作用次数、激光场强分布、激光热应力、激光支持的燃烧波和物质的蒸发波等冲击波有关。     

Pulse characteristics of Hg0.8Cd0.2Te n +-p junctions

The pulse characteristics of Hg_0.8Cd_0.2Te n ⁺-p junctions are investigated. It is shown that the shape of the voltage pulse appearing in a junction on passage of a forward (reverse) current is determined by the recombination (generation) of nonequilibrium electrons in the hole region. An increase in the current pulse causes the appearance of an electric field, which draws electrons into the interior of the base region, and leads to variation of their lifetime because of the complex structure of the n ⁺-p junction. Zh. Tekh. Fiz. 67, 130–133 (July 1997     

Experimental studies on low frequency noise of Hg0.8Cd0.2 Te photoconductors

Combined with the measurements of material characteristic parameters, detector function parameters and their temperature relation, a series of new noise experimental results on Hg_0.8Cd_0.2 Te photoconductor are obtained. The Hooge parameter from these measurements ranges from 1.7 x 10⁻³ to 8.7 x 10⁻⁵ for temperatures 90–300 K. The 1/ƒ noise spectrum increases with increasing background emission, which cannot be explained by Hooge's empirical formula. The 1/ƒ noise is less than the lower limit calculated by existing theory.     

On the activation energy of the electron liquid in Hg0.8Cd0.2Te

Recently we have shown that a magnetic field induced electron (Wigner) condensation takes places in Hg_0.8Cd_0.2Te. The correlated electrons behave like a viscous liquid with activated mobility [1]. We present the activation energy of the mobility at magnetic fields up to B = 20 T. The experimental data show that the strong increase of the activation energy with B at low fields slow down and even seems to saturate at magnetic fields above 20 T. Qualitatively this behaviour is expected for a magnetic field induced electron liquid.     

Low-temperature hot-electron energy relaxation in Hg0.8Cd0.2Te in extreme-quantum-limit magnetic fields

Energy relaxation time of hot electrons in Hg_0.8Cd_0.2Te at a lattice temperature of 1.5 K is calculated for quantizing magnetic flux densities of 4 and 6 T considering acoustic scattering via deformation potential and piezoelectric couplings. Band nonparabolicity, nonequipartition of phonons, screening of the scattering rates due to carrier space charge, and low-temperature broadening of the Landau level are incorporated. The calculated results agree qualitatively with experimental data.     

Defect related luminescence in Hg0.2Cd0.8Te nano- and micro-crystals grown by the solvothermal method

The photoluminescence (PL) properties of nano- and micro-crystalline Hg_1?xCd_xTe (x≈0.8) grown by the solvothermal method have been studied over the temperature range 10–300 K. The emission spectra of the samples excited with 514.5 nm Ar⁺ laser consist of five prominent bands around 0.56, 0.60, 0.69, 0.78 and 0.92 eV. The entire PL band in this NIR region is attributed to the luminescence from defect centers. The features like temperature independent peak energy and quite sensitive PL intensity, which has a maximum around 50 K is illustrated by the configuration coordinate model. After 50 K, the luminescence shows a thermal quenching behavior that is usually exhibited by amorphous semiconductors, indicating that the defects are related to the compositional disorder.     

Resonant 2D magnetopolarons in accumulation layers on n-Hg0.8Cd0.2Te

Cyclotron Resonance measurements on accumulation-layer electrons at anodic oxide films on n-(Hg,Cd)Te are reported. Up to six subband cyclotron resonances are observed and discontinuities are seen in the subband effective masses, due to resonant polaron effects. The coupling is strongest for the higher subbands, where it is enhanced over that for the bulk, and occurs at the “HgTe-like” LO phonon frequency. The behaviour of the lowest (i=0,1) subbands is more complex, with the coupling being weaker and the dominant interaction seeming to occur at the TO frequency for low values of N_S.     

X-ray Diffraction Study of Cd 0.8 Zn 0.2 Te Under High Pressure and Temperature

Energy dispersive X-ray diffraction using synchrotron radiation has been used to study phase transformations of Cd 0.8 Zn 0.2 Te under high pressure and temperature. We confirm the presence of a cinnabar phase between the zinc-blende and rock-salt phases. But contrary to the results in CdTe, this intermediate phase is found to be stable only on pressure decrease and in a narrower pressure and temperature range. Single-phase cinnabar patterns are obtained only at 300 and 373 K. At 673 K and above, even on pressure decrease, no evidence of the cinnabar phase is found. In this temperature range, a phase segregation phenomenon is observed in the zinc-blende phase during the zinc-blende transition in both upstroke and downstroke, and the retrieved sample at ambient conditions presents a double pattern corresponding to two different Zn contents.     

Two-dimensional electron systems in inversion layers of p-type Hg0.8Zn0.2Te metal-insulator-semiconductor structures

Strong oscillations on capacitance and conductance have been observed in p-type Hg0.8Zn0.2Te metal-insulator-semiconductor structures, made by using a recent process for the interface passivation. This behaviour is attributed to a two-dimensional electron gas in the n-inversion layer and the variation of the conductance maximums with temperature indicates that the dominant perpendicular transport mechanism for electrons is an incoherent two-step tunnelling through deep levels in the gap. Three models have been used to describe the quantum confinement: the simple variational method, the triangular potential approximation and the propagation matrix method. The later approach takes into account the non parabolicity of the conduction band structure and uses a finite height barrier at the insulator-semiconductor interface. A very good agreement between experimental and calculated values for the two lowest subband energy is obtained. Received 9 February 1999     

High conversion efficiency Hg0.77Cd0.23Te spin-flip Raman laser

Peak external conversion efficiencies of several percent have been measured in the 10 μm region when a CO₂ laser is used to pump a Hg_0.77Cd_0.23Te spin-flip Raman laser. Strong pump depletion is observed in the experiments. Quantum oscillations from the n = 0, 1 and 2 Landau levels are observed in the tuning characteristics. At 710 G the spontaneous linewidth is measured to be 8 G. Large effects due to conduction band nonparabolicity are observed.     

Ferroelectric switching behavior of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films

The effect of pulse amplitude on the ferroelectric and switching properties of pulsed laser deposited Ba_0.8Sr_0.2TiO₃ thin films has been studied. The structural and morphological analysis revealed that the films had a well crystallized perovskite phase and grain size of about 30–40 nm. A well saturated P–E hysteresis loop was observed with a remnant polarization (P_r) ≈ 4.8 μC/cm² and a coercive field ≈ 100 kV/cm at a frequency of 1 kHz. The P_r has been found to be decreased only 4.3% after passing 8.0 × 10⁸ cycles. The analysis of switching response with nucleation limited switching model reveals that characteristic switching time (t₀) variance is due to the random distribution of the local electric fields. The peak value of polarization current and t₀ exhibits exponential dependence on reciprocal of pulse amplitude.     

Free exciton luminescence lineshape of Hg0.3Cd0.7Te

The photoluminescence spectrum of Hg_0.3Cd_0.7Te at 77K includes a narrow, high energy free exciton line. This experimental spectrum is in good agreement with the theoretical free exciton lineshape, the Gaussian broadening of this line is due to alloy inhomogeneity, and the binding energy of the bound exciton with respect to the free exciton at 77K is 13 ± 4 meV.     

分子束外延HgCdTe材料的光致发光研究

报道了分子束外延生长 Ｈｇ０．６８ Ｃｄ０．３２ Ｔｅ 材料的光致发光测量结果。研究了原生样品和退火处理样品、以及氮离子注入样品的低温光致发光特征。对光致发光的测试结果进行拟合得到的禁带宽度, 与用红外透射谱得到的薄膜禁带宽相近; 其半峰宽和带尾能量较小, 显示了较高的薄膜质量。样品经过退火后带尾能量降低, 双晶衍射的半峰宽也有明显的变窄     

纳秒脉冲激光沉积薄膜过程中的烧蚀特性研究

研究了高能短脉冲激光薄膜制备的整个烧蚀过程.首先建立了基于超热理论的烧蚀模型，然 后利用较为符合实际的高斯分布表示脉冲激光输入能量密度，给出了考虑蒸发效应不同阶段 的烧蚀状态方程.结合适当的边界条件，以Si靶材为例，利用有限差分法得到了靶材在各个 阶段温度随时间和烧蚀深度的演化分布规律及表面蒸发速度与烧蚀深度在不同激光辐照强度 下随时间的演化规律.结果表明，在脉冲激光辐照阶段，靶材表面的蒸发效应使得靶材表面 温度上升显著放缓；在激光辐照强度接近相爆炸能量阈值时，蒸发速度与蒸发厚度的变化由 于逆流现象将显著放缓.还得到了考虑了熔融弛豫时间及蒸发效应的固-液界面随时间的演化 方程，这一结论较先前工作更具有普适性. 关键词： 脉冲激光烧蚀 热流方程 温度演化 有限差分法