Device fabrication on epitaxial Si-Ge alloys

PMOS transistors, p-n junctions and diffused resistors have been fabricated in Si-Ge alloy having a range of Ge content from 0 to 38%. The p-n junctions showed lower forward voltage drops than one would expect from simple band-gap lowering information. A Ge build-up at the surface may be causing this. MOS transistors exhibited low mobilities in the range of 20–50 cm²/V-s. The mobility value was affected by the surface condition and smoother surface areas resulted in the higher values of mobility. Diffused resistors had very high resistor values compared to control samples fabricated on silicon. Contact resistance problems were suspected but not proved to be the cause.     

Strain evolution and dopant activation in P-lmplanted metastable pseudomorphic Si(100)/Ge0.12Si0.88

A metastable Ge_0.12Si_0.88 layer 265 nm thick was deposited pseudomorphically on a Si(100) substrate and then implanted with 100 keV phosphorus ions at room temperature for doses of 5 × 10¹³/cm² to 1.5 × 10¹⁵/cm². The ions stop within the epilayer (projected range ∼125 nm). MeV⁴He backscattering/channeling spectrometry, transmission electron microscopy, and double-crystal x-ray diffractometry were used to characterize the damage and strain in the films. The samples were subsequently annealed in high vacuum from 400-800°C for 30 min at each temperature. For the nonamorphized samples (doses of 5 and 10 × 10¹³/cm²), most of the implantation-induced damage and strain disappear after annealing at 400-550°C, but the implanted P ions activate poorly. After annealing at 700-800°C, near complete activation is achieved but the strain relaxes. For the amorphized samples (dose of 1.5 × 10¹⁵/cm²), the amorphous GeSi regrows by solid-phase epitaxy and the dopants are ∼100% activated after annealing at 550°C, but the regrown GeSi relaxes with a high density of dislocations. The strain relaxes more extensively upon annealing in an implanted sample than in a nonimplanted one, other conditions being equal. This effect is more pronounced at higher ion doses, probably due to the increased amount of damage introduced at high doses. On leave from Yonsei University, Seoul 120-749, Korea     

Phonon-resolved and broad photoluminescence in strained Si1−xGex alloy MBE layers

In the photoluminescence (PL) spectra of Si_1?xGe_x multi-quantum wells (MQW) grown by conventional solid source molecular beam epitaxy (MBE), phonon-resolved, near-bandgap transitions due to shallow dopant bound exciton or free exciton recombination were observed when the well thickness was less than 40–100Å, depending on x. Increasing the Si_1?xGe_x well thickness caused the emergence of a broad, unresolved PL peak ～120 meV lower in energy than the expected bandgap energy. Interstitial-type platelets, less than 15Å in diameter, were measured by plan view transmission microscopy to occur in densities that correlated well with the intensity of the broad PL peak. A platelet density of ～10⁸ cm^?2 per well was sufficient to completely quench the phonon-resolved PL. Etching experiments revealed that within a given MQW, the platelet density is lowest in the first grown well and progressively increases in subsequent wells with increasing strain energy density, indicating that platelet formation is strictly a morphological phenomenon and suggesting that a strain relaxation mechanism is in effect before the onset of relaxation by misfit dislocation injection.     

硅-锗合金废料中锗的回收研究

研究了硅-锗合金废料中锗的回收,采用碳酸钠+Na2O2熔融-磷酸中和-盐酸蒸馏法,并对工艺进行了优化。该工艺具有回收率高、成本低、环境友好等优点。     

SiO2衬底上PECVD-Si1-xGex薄膜研究

在覆盖SiO2的n-Si(100)衬底上,采用等离子体增强化学沉积法(PECVD)制备Si1-xGex薄膜材料。薄膜Ge含量x及元素的深度分布由俄歇电子谱(AES)测定。对Si1-xGex进行热退火处理,以考察退火温度和时间对薄膜特性的影响。薄膜的物相通过X射线衍射(XRD)确定。基于XRD图谱,利用Scherer公式计算平均晶粒大小。Si1-xGex薄膜载流子霍尔迁移率由霍尔效应法测定。数值拟合得到霍尔迁移率与平均晶粒尺寸为近线性关系,从而得出PECVD-Si1-xGex薄膜的电输运特性基本符合Seto模型的结论。     

Photoluminescence spectra of Si1-xGex/Si quantum well structures grown by three different techniques

Photoluminescence (PL) spectra of Si_1-xGe_x/Si multiple quantum wells have been measured at 4.2 K for the samples grown by three different techniques; conventional molecular beam epitaxy (MBE), gas-source MBE, and ultra high vacuum chemical vapor deposition (UHV-CVD). Only in the case of conventional MBE, strong emission bands appear about 80 meV below the band gap of Si_1-xGe_x. These strong emission bands disappear after the annealing at 800° C. From the dependence of the PL intensity on the excitation power, strong emission is considered to be due to some recombination center. On the other hand, in the case of gas-source MBE and UHV-CVD, the strong emission bands are undetectable, although the band-edge PL lines of Si_1-xGe_x are clearly observed. There is no significant change in the PL spectra after the annealing. The origin of the strong emission band is considered to be defects which are characteristic of conventional MBE.     

超高真空化学气相沉积外延生长锗硅材料及其应用

综述了硅基锗硅薄膜的外延生长技术、设备及其在光电子器件上的应用,其中着重介绍了超高真空化学气相沉积系统(UHVCVD)。目前来说,UHVCVD是产业化制备高质量锗硅材料的最佳选择。     

Ion beam mixing of silicon-germanium thin films

An overview of processing silicon-germanium (Si-Ge) alloys for various applications is presented here. Several methods of formation are briefly summarized. In particular, results of preliminary experiments on ion-beam mixing of Si-Ge layered structures deposited by physical vapor deposition and subsequently ion implanted with varying doses of argon are presented. Different layered structures have been designed and mixed to obtain optimal process conditions. The ion beam mixing process yields films with a gradual band-gap variation from 1.12 eV to 0.85 eV, thus allowing quite a wider spectrum of wavelengths to be absorbed. Rutherford backscattering spectrometry (RBS) has been used to characterize the nature and extent of the mixing of as-deposited and irradiated films.     

Application of the parametric bootstrap method to determine statistical errors in quantitative X-ray microanalysis of thin films

We applied the parametric bootstrap to the X‐ray microanalysis of Si‐Ge binary alloys, in order to assess the dependence of the Ge concentrations and the local film thickness, obtained by using previously described Monte Carlo methods, on the precision of the measured intensities. We show how it is possible by this method to determine the statistical errors associated with the quantitative analysis performed in sample regions of different composition and thickness, but by conducting only one measurement. We recommend the use of the bootstrap for a broad range of applications for quantitative microanalysis to estimate the precision of the final results and to compare the performances of different methods to each other. Finally, we exploited a test based on bootstrap confidence intervals to ascertain if, for given X‐ray intensities, different values of the estimated composition in two points of the sample are indicative of an actual lack of homogeneity.     

Solid boron and antimony doping of Si and SiGe grown by gas source molecular beam epitaxy

Solid boron and antimony doping of silicon and SiGe grown by molecular beam epitaxy using disilane and germane as sources has been studied. Elemental boron is a well behaved p-type dopant. At effusion cell temperatures of 1700–1750°C, hole carrier concentrations in the 10²⁰ cm⁻³ range have been obtained. Elemental antimony doping shows surface segregation problems. For uniformly doped layers, the as-grown materials do not show n-type conductivity. Electron concentrations in the 10¹⁷ cm⁻³ range were obtained by post-growth conventional and rapid thermal annealing at 900 and 1000°C, respectively. The electron Hall mobility improves with optimum annealing time. Delta doping of buried layers exhibits slightly better incorporation behavior including significant surface riding effects.