G. W. Huang

Phosphorus doping of Si and Si1−xGex grown by ultrahigh vacuum chemical vapor deposition using Si2H6 and GeH4

100 ppm PH3 diluted in hydrogen is used as the n‐type dopant gas in Si and Si1−xGex epilayers grown by ultrahigh vacuum chemical vapor deposition (UHVCVD) using Si2H6 and GeH4. The phosphorus concentration in Si increases linearly at a small PH3 flow rate and becomes nearly saturated at higher flow rates, while the phosphorus concentration in Si1−xGex only shows a nearly linear behavior with PH3 flow rate. The growth rates of Si and Si1−xGex epilayers decrease seriously (∼50%) and slightly (∼10%) with the increase of PH3 flow rate, respectively. These results can be explained by a model based on the enhancement of hydrogen desorption rate at smaller PH3 flow rates and different levels of the effects of phosphorus blocking of surface‐activated sites between Si and Si1−xGex epilayers at higher PH3 flow rates.

Direct Oxidation of Si1¡xGex Layers Using Vacuum-Ultra-Violet Light Radiation in Oxygen

The fabrication of many novel devices has placed strong requirements of the use of new materials such as strained epitaxial Si1ixGex layers. The advantages of the SiGe-base system over other compound semiconductor systems is its compatibility with Si technology and the possibility of very large scale integrated (VLSI) circuits fabrications. Moreover, the hole mobility 1) of SiGe is higher than that of Si. The

Boron incorporation in Si1−xGex films grown by ultrahigh vacuum chemical vapor deposition using Si2H6 and GeH4

0.1% B2H6 diluted in hydrogen is used as the p‐type dopant gas in Si1−xGex grown by ultrahigh vacuum chemical vapor deposition (UHVCVD) using Si2H6 and GeH4. The boron concentration is evaluated by secondary ion mass spectrometry (SIMS). The boron concentration of Si1−xGex increases with the increase of the GeH4 flow rate, that is, Ge fraction, by keeping Si2H6 and B2H6 flow rates constant. The result may be due to the increase of the vacant surface sites which is caused by the increase of the hydrogen desorption rate when a higher Ge fraction epilayer is grown.

Low temperature epitaxy of Si and Si1−xGex by utrahigh vacuum-chemical molecular epitaxy

Pure Si2H6 and GeH4 are used to grow Si and Si1−xGex epilayers at 550 °C by ultrahigh vacuum-chemical molecular epitaxy. 0.1% B2H6 and 100 ppm PH3 diluted in H2 are used as the p- and n-type dopant gases in Si/Si1−xGex epitaxy. The Ge mole fraction x and the growth rate of Si1−xGex epilayers show very strong dependence on the total source gas flow rate ([GeH4]+[Si2H6]) and the source gas ratio ([GeH4]/[GeH4]+[Si2H6]). The results can be explained by the relationships of the source fluxes, relative incorporation efficiency at activated surface sites, and hydrogen desorption under different growth conditions. The boron concentration of Si1−xGex increases with increasing GeH4 flow rate by keeping Si2H6 and B2H6 flow rates constant. It may be due to the increase of the surface sites which is caused by the increase of the hydrogen desorption rate when a higher Ge mole fraction epilayer is grown. The phosphorus concentrations of Si and Si1−xGex show different behavior with PH3 flux at higher PH3 flow rates whil...

RF MOSFET Characterization by Four-Port Measurement

RF MOSFETs are usually measured in common source configuration by a 2-port network analyzer, and the common gate and common drain S-parameters cannot be directly measured from a conventional 2-port test structure. In this work, a 4-port test structure for on-wafer measurement of RF MOSFETs is proposed. Four-port measurements for RF MOSFETs in different dimensions and the de-embedded procedures are performed up to 20 GHz. The S-parameters of the RF MOSFET in common source (CS), common gate (CG), and common drain (CD) configurations are obtained from a single DUT and one measurement procedure. The dependence of common source S-parameters of the device on substrate bias are also shown.

Noise parameters computation of microwave devices using genetic algorithms

In this letter, a new computation method for the noise parameters of a linear noisy two-port network is introduced. A new error function, which considers noise figure and source admittance error simultaneously, is proposed to estimate the four noise parameters. The global optimization of the error function is searched directly by using a genetic algorithm.

Epitaxy of Si1-xGex by Ultrahigh-Vacuum Chemical Vapor Deposition Using Si2H6 and GeH4

Disilane and germane were used to grow Si1-x Gex epilayers at 550° C by ultrahigh-vacuum chemical vapor deposition (UHVCVD). The solid composition x and growth rate of Si1-x Gex were evaluated from double-crystal X-ray rocking curves and show very strong dependence on the total source gas flow rate ( [ GeH4]+[Si2H6]) and the gas ratio ( [GeH4]/[GeH4]+[Si2H6]). The solid composition increases with increase of the gas ratio and also with increasing the total source flux by keeping gas ratio constant. The growth rate increases with the solid composition at lower values and then becomes saturated in the higher composition range (x>0.22). The results can be explained by the relationships of the source fluxes, relative incorporation efficiency at activated surface sites and hydrogen desorption under different growth conditions.

Abruptness of Ge composition at the Si/SiGe interface grown by ultrahigh vacuum chemical vapor deposition

A model is proposed to estimate the interfacial abruptness of the Si/SiGe heterojunction. In this model, a transition region with linearly graded Ge composition is assumed at the Si/SiGe interface. The Ge composition x of Si/SiGe quantum well grown by ultrahigh vacuum chemical vapor deposition at 550 °C is found to increase with the deposition time as deposition at the same gas phase composition. This phenomenon can be explained by this model and the fitting results match the measured data. The thickness of the transition region and the transition time can be extracted from these fittings. The transition thicknesses are found to be about 1.9 nm or thinner as grown at 550 °C or below.

CHARACTERIZATION OF SI/SIGE STRAINED-LAYER SUPERLATTICES GROWN BY AN ULTRAHIGH-VACUUM CHEMICAL-VAPOR-DEPOSITION TECHNIQUE

High-resolution double-crystal X-ray diffraction and cross-sectional transmission electron microscopy were used to characterize the Si/SiGe strained-layer superlattices grown by the ultrahigh vacuum/chemical vapor deposition (UHV/CVD) system. A dynamical X-ray simulation was employed to analyze the experimental rocking curves. Good matches between the experimental rocking curves and the simulated ones demonstrate that the high quality Si/SiGe strained-layer superlattices with abrupt interface and excellent thickness and composition uniformity have been achieved. Thickness uniformity was further confirmed by the cross-sectional transmission electron microscopy. In addition, high-resolution double-crystal X-ray diffraction was proven to be a powerful technique for determining the doping level and the thickness of heavily doped contact layer in Si/SiGe device structures prior to further processing. Good wafer-to-wafer uniformity can be simultaneously achieved by the UHV/CVD technique; as a result, the UHV/CVD technique is readily applicable to manufacturing.

Characterization of the Si/SiGe heterojunction diode grown by ultrahigh vacuum chemical vapor deposition

The unipolar Si/SiGe heterojunction diode grown by ultrahigh vacuum chemical vapor deposition at 550 °C is demonstrated. The dark current density measured at 77 K is (2.5±0.1)×10−7 A/cm2 for the barrier height of 176±8 meV, at a reverse bias of 1 V. The barrier heights are measured from the activation analysis of the saturation current and compared to the theoretical values. The barrier height decreases as the thickness of the SiGe strained layer exceeds the critical thickness.