Temperature-dependent characteristics of a reach-through avalanche photodiode (RAPD) in Ge,Si and GaAs

A theoretical assessment is presented based on a modification of Baraff's theory in order to compare the temperature dependence of several characteristics, including breakdown voltage, excess noise factor, effective ionization rate ratio and efficiency in Ge, Si and GaAs reach-through avalanche photodiodes (RAPD). The temperature coefficient of avalanche breakdown voltage in a depletion region is studied. The response time of a reach-through APD in these materials is also discussed. Finally a comparison of the characteristics between PIN APD and RAPD is presented. The theoretical data have also been substantiated experimentally by Kanedaet al. Supported by National Science Council, the Republic of China     

Temperature dependent characteristics of submicron GaAs avalanche photodiodes obtained by a nonlocal analysis

In this paper, using a nonlocal analysis we have extracted the temperature dependent ionization coefficients and threshold energies of submicron GaAs avalanche photodiodes (APDs) with multiplication region thicknesses as narrow as 49 nm, from electron and hole injection photo-multiplication processes. These extracted parameters have been used to predict the temperature dependence of APDs characteristics, such as mean gain, 3 dB-bandwidth, gain-bandwidth product, excess noise factor, performance factor, and breakdown field, over a temperature range of 20 K to 290 K. In the nonlocal analysis we have taken the effects of nonuniform electric filed within the multiplication region and its surrounding depletion regions, injected carrier’s initial ionization energy, carrier’s spatial ionization rate as well as the carrier’s dead space and its previous ionization history into account. We have shown that our predicted gain values are in excellent agreement with existing experimental data measured by others.     

Noise characteristics of a superlattice avalanche photodiode

The noise generated due to randomness of multiplication process in the avalanche region of an Al _x Ga_1–x As/GaAs quantum well p⁺-i-n⁺ structure has been studied. The paper presents a quantitative evaluation of the noise performance of the superlattice APD which has not been done so far. Further, useful design data for low noise structure is given.     

Modeling the effects of interface traps on passive quenching of a Ge/Si geiger mode avalanche photodiode

The influence of interface donor and acceptor traps on the behavior of Ge/Si separate absorption, charge and multiplication Geiger mode avalanche photodiodes under passive quenching is modeled. The effects of different trap types on the quenching behavior are investigated in this paper for the first time. Our results show that trap type and trap density significantly influence the APD quenching time and ability to quench for a particular quenching resistor.     

Electronic states of (2 × 1) and (1 × 1) (111) surfaces of Ge,Si, diamond,GaAs and Ge on Si

The “dangling-bond” surface state dispersion curves, E(k), have been calculated for the (2 × 1) and (1× 1) (111) surfaces of Ge, Si, and diamond, for (1 × 1) GaAs, and for (2 × 1) Ge on Si. The calculations employ the sp³s1 empirical tight-binding model of Vogl et al. and the atomic relaxation of Feder et al. The surface state band gaps are in good agreement with optical-absorption and electron-energy-loss measurements for Ge and Si. For the assumed epitaxial geometry, Ge on Si is predicted to shift the dangling-bond states downward by ≈0.1 to 0.4 eV.     

High pressure solid state amorphization of Si,Ge and solid solutions Si:GaAs,Ge:GaSb

Abstract

The bulk amorphous tetrahedral semiconductors (Si, Ge. Si_0.89(GaAs)_0.11, Ge_1?x(GaSb)_x (0.12<X<I)) were obtained using solid state amorphization. The disordering process occurs at the decompression of high pressure phases Si II, Gell at low temperatures and of solid solutions Sill: GaAs, GeII: GaSb at room temperature. The structure and stability of the obtained phases were investigated     

Self-diffusion of (31)Si and (71)Ge in relaxed Si(0.20)Ge(0.80) layers

Self-diffusion of implanted (31)Si and (71)Ge in relaxed Si(0.20)Ge(0.80) layers has been studied in the temperature range 730-950 degrees C by means of a modified radiotracer technique. The temperature dependences of the diffusion coefficients were found to be Arrhenius-type with activation enthalpies of 3.6 eV and 3.5 eV and preexponential factors of 7.5 x 10(-3) m(2) s(-1) and 8.1 x 10(-3) m(2) s(-1) for (31)Si and (71)Ge , respectively. These results suggest that, as in Ge, in Si(0.20)Ge(0.80) both (31)Si and (71)Ge diffuse via a vacancy mechanism. Since in Si(0.20)Ge(0.80) (71)Ge diffuses only slightly faster than (31)Si , in self-diffusion studies on Si-Ge (71)Ge radioisotopes may be used as substitutes for the "uncomfortably" short-lived (31)Si radiotracer atoms.     

Cluster model approach for electronic structure of Si and Ge(111) and GaAs(110) surfaces

For the purpose of exploring how realistic a cluster model can be for semiconductor surfaces, extended Huckel theory calculations are performed on clusters modeling Si and Ge(111) and GaAs(110) surfaces as prototypes. Boundary conditions of the clusters are devised to be reduced. The ideal, relaxed, and reconstructed Si and Ge(111) surfaces are dealt with. Hydrogen chemisorbed (111) clusters of Si and Ge are also investigated as prototypes of chemisorption systems. Some comparison of the results with finite slab calculations and experiments is presented. The cluster-size dependence of the calculated energy levels, local densities of states, and charge distributions is examined for Si and Ge(111) clusters. It is found that a 45-atom cluster which has seven layers along the [111] direction is large enough to identify basic surface states and study the hydrogen chemisorption on Si and Ge(111) surfaces. Also, it is presented that surface states on the clean Si and Ge(111) clusters exist independent of relaxation. Further, the calculation for the relaxed GaAs(110) cluster gives the empty and filled dangling-orbital surface states comparable to experimental data and results of finite slab calculations. The cluster approach is concluded to be a highly useful and economical one for semiconductor surface problems.     

Size dependent charge storage characteristics of MBE grown Ge nanocrystals on surface oxidized Si

We have demonstrated the growth of size controlled Ge nanocrystals by molecular beam epitaxy on oxidized Si for the fabrication of floating gate memory structure. The size and density of the nanocrystals have been controlled by varying the growth temperature. The role of interface states and nanocrystals on the memory characteristics has been studied using frequency dependent conductance-voltage measurements. Superior retention characteristics and an enhanced memory window width have been achieved by replacing SiO₂ with high-k Al₂O₃ as a blocking oxide with a higher barrier height.     

高性能SOI基GePIN波导光电探测器的制备及特性研究

本文报道了在SOI衬底上外延高质量单晶Ge薄膜并制备高性能不同尺寸Ge PIN波导光电探测器.通过采用原子力显微镜、X射线衍射、拉曼散射光谱表征外延Ge薄膜的表面形貌、晶体质量以及应变参数,结果显示外延Ge薄膜中存在约0.2%左右的张应变,且表面平整,粗糙度为1.12 nm.此外,通过暗电流、光响应度以及3 dB带宽的测试来研究波导探测器的性能,结果表明尺寸为4μm×20μm波导探测器在-1 V的反向偏压下暗电流密度低至75 mA/cm~2,在1.55μm波长处的响应度为0.58 A/W,在-2 V的反向偏压下的3 dB带宽为5.5 GHz.     

Comparison of Si and Ge low-loss spectra to interpret the Ge contrast in EFTEM images of Si(1-x) Ge(x) nanostructures

Recently, an EFTEM imaging method, exploiting the inelastically scattered electrons in the 60-90eV energy range, was proposed to visualise Ge in SiGe alloys [Pantel, R., Jullian, S., Delille, D., Dutartre, D., Chantre, A., Kermarrec, O., Campidelli, Y., Kwakman, L.F.T.Z., 2003. Inelastic electron scattering observation using Energy Filtered Transmission Electron Microscopy for silicon-germanium nanostructures imaging. Micron 34, 239-247]. This method was proven to be highly more efficient in terms of noise, drift and exposure time than the imaging of the weak and delayed ionization GeL2,3 edge at 1236eV. However, the physical phenomenon behind this Ge contrast was not clearly identified. In this work, we explain the origin of this Ge contrast, by comparing in details EELS low-loss spectra (<100eV) recorded from pure Si and Ge crystals. High resolved low-loss experiments are performed using analytical Field Emission Gun Transmission Electron Microscopes fitted or not with a monochromator. Low-loss spectra (LLS) are then deconvoluted from elastic/quasi-elastic and plural scattering effects. The deconvolution procedure is established from Si spectra recorded with the monochromated machine. The absence of second plasmon and the measurement of a band gap (1.12eV) on the Si single scattering distribution (SSD) spectrum allowed us to control the accuracy of the deconvolution procedure at high and low energy and to state that it could be reliably applied to Ge spectra. We show that the Ge-M4,5 ionisation edge located at 29eV, which is shadowed by the high second plasmon in the unprocessed Ge spectrum, can be clearly separated in the single scattering spectrum. We also show that the front edge of Ge-M4,5 is rather sharp which generates a high intensity post edge tail on several tens of eV. Due to this tail, the Si and Ge EELS signals in the 60 to 100eV energy window are very different and the monitoring of this signal gives information about the Ge concentration inside SiGe alloys. It is now evident that the EFTEM imaging technique proposed to quantify Ge (90eV/60eV image ratio) in Si-Ge nanostructures is valid and is a relevant way of exploiting the Ge-M4-5 ionisation edge.     

Ge self-diffusion in epitaxial Si(1)-(x)Ge(x) layers

Diffusion coefficients and activation energies have been determined for Ge diffusion in strain-relaxed Si(1)-(x)Ge(x) with x = 0.00, 0.10, 0.20, 0.30, 0.40, and 0.50. The activation energy drops from 4.7 eV in Si and Si(0.90)Ge(0.10) to 3.2 eV at x = 0.50. This value compares with the literature value for Ge self-diffusion in Ge, suggesting Ge-like diffusion already at x approximately equal to 0.5. The effect of strain on the diffusion was also studied showing a decrease in diffusion coefficient and an increase in activation energy upon going from compressive over relaxed to tensile strain.     

Temperature dependent low energy electron microscopy study of Ge growth on Si(1 1 3)

We investigated the initial Ge nucleation and Ge island growth on a Si(1 1 3) surface using low energy electron microscopy and low energy electron diffraction. The sample temperature was varied systematically between 380 °C and 590 °C. In this range, a strong temperature dependence of the island shape is observed. With increasing temperature the Ge islands are elongated in the direction. Simultaneously, the average island size increases while their density decreases. From the Arrhenius-like behaviour of the island density, a Ge adatom diffusion barrier height of about 0.53 eV is deduced.     

Room temperature oxidation of Cu(3)Ge films grown on Si and Si(1-x)Ge(x) substrates

Room temperature oxidation of Cu3Ge films grown on Si, Si(0.85)Ge(0.15) and Si(0.52)Ge(0.48) substrates, respectively, at a temperature of 200-300 degrees C was studied using transmission electron microscopy (TEM) in conjunction with energy dispersive spectrometry (EDS) and scanning electron microscopy (SEM). For Cu(3)Ge films grown at 200 degrees C and subsequently exposed in air for 1 week oxide protrusions and oxide networks appeared in the film surface and grain boundaries of Cu(3)Ge, respectively. At room temperature O from air and Si from the substrate, diffused along the grain boundaries of Cu(3)Ge to react with Cu(3)Ge grains, initiating the Cu(3)Si-catalyzed oxidation. Cu(3)Ge films are superior to Cu(3)(Si(1-x)Gex) films in retarding Cu(3)Si-catalyzed oxidation. Annealing at 300 degrees C allowed Si diffusion from the substrate into the Cu(3)Ge overlayer to form Cu(3)(Si(1-x)Gex), enhancing the Cu(3)Si-catalyzed oxidation rate. In the present study, Cu(3)Ge films grown on Si(0.52)Ge(0.48) at 200 degrees C show the best resistance to room temperature oxidation because higher Ge concentration in the substrate and lower temperature annealing can more effectively retard Si diffusion from the substrate into the Cu(3)Ge overlayer, and hence reduce the Cu(3)Si-catalyzed oxidation rate.