Phosphorus doping

Figures High mass resoiution mass spectrum obtained from a phosphorus-doped amorphous silicon hydride thin film using a magnetic sector ion microanalyzer. The peak is well separated from the hydride iirterferences.

Mulder, J., Eppenga, P., Hendriks, M., and Tong, J., An Industrial LPCVD Process for In Situ Phosphorus-Doped Poly silicon, /. Electrochem. Soc., 137(l) 273-279(Jan. 1990)... 

Fig. 20. Hydrogen diffusion coefficient, measured at 240°C, for 0.1% phosphorus doped a-Si H, as a function of the substrate temperature for which the samples were grown (Street and Tsai, 1988). 

Figure 5.16. SIMS of a solution-processed phosphorus-doped a-Si film. The phosphorus concentration in the films is almost proportional to that of the initial solutions in the case of the copolymerized method. [Reproduced with permission from Ref. 25. Copyright 2007 The Japan Society of Applied Physics.]...

Figure 6.34 Electrical conductivity and dielectric susceptibility of phosphorus-doped silicon at T 10" K. The dielectric susceptibility shows a divergence as the transition is approached from the insulator side. Notice the sharp, but continuous threshold in a(n) on the metallic side. (After Hess et ai,...

Since Si02 substrates appear frequently during IC fabrication, the adhesion test results for this substrate are important. Four types of oxides have been extensively tested. They are (1) thermal oxide grown at 7>1000°C, (2) softer oxide processed by conventional spin-on-glass technology, (3) phosphorus-doped LPCVD oxide, and (4) low-temperature (200°C) plasma deposited oxide. 

Effects of Silicon Doping. Silicon heavily doped with donor or acceptor impurities can exhibit oxidation rates that are considerably enhanced relative to lightly doped silicon (84,112). For example, the dependencies of the rate constants on substrate phosphorus doping level are shown in Figure 31 for oxidations of <111> silicon at 900 °C. B/A increases sharply by more than an order of magnitude as the phosphorus level increases beyond lO /cm3. 

The temperature dependence of the linear rate constants for various electron concentrations in phosphorus-doped silicon indicate that the doping has only a slight effect on the associated activation energy. Thus, because B/A is proportional to the rate of the interface reaction, the doping effect is buried in the chemical, electrical, or, possibly, mechanical dependence of surface rate on doping. 

It has been suggested that when phosphorus-doped polycrystalline silicon is produced by LPCVD of SiH4-PH3 mixtures, gaseous SiH2 that reaches the surface becomes the dominant contributor to film formation383. It seems, however, that the quality of the films deposited by LPCVD from SilI4 increases if gas-phase decomposition, and hence SiH2 formation, decreases . 

A 1 ym thick polycrystalline silicon (polysilicon) layer was then deposited by chemical vapor deposition (CVD). Phosphorus doping of polysilicon was done by ion implantation with a dosage of 1Cr° cm-2 and a voltage of 200 keV. The polysilicon sheet resistance of 50 SI/ was obtained after post-implant activation (Figure 1a). 

A phosphorus-doped polysilicon layer was used as the sensor heater. Its temperature coefficient of resistivity was positive with a value of 6 x 10 4°C 1. The value of the heater resistance as a function of temperature was used to indicate the sensor temperature. 

Again, a low-pressure, hot-wall CVD reactor was used for the depositions. Pressures ranged from 300 to 900 mTorr. Phosphorus doping was carried out with trimethylphosphite. For these experiments, some depositions were carried out with oxygen addition. In this case, deposition rates were lowered. Combining trimethylphosphite with oxygen, on the other hand, increased deposition rates. 

Meyerson, B.S., and Olbricht, W., Phosphorus-doped polycrystalline silicon... 

This basic system was designed to deposit Si02 from the SiH4 + 02 reaction at about 400°C and atmospheric pressure. It can also deposit doped oxides by introducing PH3 for phosphorus doping or B2H6 for boron doping. In order to protect personnel from these toxic dopants, the reactor is housed in a vented enclosure. 

A typical silicon PV cell is composed of a wafer consisting of an ultra-thin layer of phosphorus-doped silicon (N-layer with a negative character). 

The net result is that doped a-Si H films are not very conductive (typically 10-3-10-2 Q-1 cm-1)- The Fermi level is — 0.2 eV below the conduction band in phosphorus-doped a-Si H (Spear, 1977) and is—0.5 eV above the valance band in boron-doped a-Si H (Jan et al., 1980). Since the optical gap of undoped a-Si H is typically about 1.7 eV, the built-in potential of a-Si Hp-i-n solar cells is about 1.0 eV (Williams et al., 1979). Improving the conductivity of the doped layers should lead to larger built-in potentials and consequently higher conversion efficiencies. The conductivity can be increased significantly by forming microcrystalline-doped Si H films (Mat-suda et al., 1980), but since these films contain both amorphous and crystalline phases, there is no significant increase in the built-in potential (Carlson and Smith, 1982). 

The photoconductivity increases when the a-Si H is lightly doped with phosphorus (Anderson and Spear, 1977). However, phosphorus doping causes very slow decay of photoresponse. The photoresponse characteristic for the phototconductive sensor using undoped a-Si H is shown in Fig. 3. The illumination is the modulated light from a GaP LED. The modulation ratio is defined as M = (it — i2)/i2, where is the peak photocurrent and i2 is the bottom current just prior to the next pulse. Figure 4 shows the modulation ratio of a-Si H versus the pulse width T, compared to that of the CdS-CdSe photoconductive sensor. The CdS-CdSe sensor modulation ratio decreases as the repetition time becomes shorter. On the other hand, in the a-Si H photoconductive sensor, the modulation ratio does not decrease... 

Optical absorption spectra of as-grown and laser-annealed areas are shown in Fig. 11 for an undoped and a B-doped a-Si H film (Staebler, 1979). Phosphorus-doped films have an absorption characteristic straddling between the undoped and the boron-doped films but showed additional illumination effects. These curves revealed that all films darken on exposure... 

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