Phosphorus doping silicon with

Silicon s atomic structure makes it an extremely important semiconductor. Highly purified silicon, doped with such elements as boron, phosphorus, and arsenic, is the basic material used in computer chips, transistors, sUicon diodes, and various other electronic circuits and electrical-current switching devices. Silicon of lesser purity is used in metallurgy as a reducing agent and as an alloying element in steel, brass, and bronze. 

So far we have considered only pure, one-component systems. When a solute dissolves in such a system, it produces a solution—a homogeneous mixture of two or more components—which can be solid, liquid, or gas. The solute affects the physical properties of the solvent. Solid solutions of solutes in metalloid and nonmetal solvents, such as silicon doped with a tiny amount of phosphorus as solute, exhibit electrical properties that make them the primary materials of the electronics industry (Section 3.13). When we spread salt on icy sidewalks, we are creating a mixture of salt and water that lowers the freezing point of water. If that temperature is lower than the ambient temperature, the ice melts. Gaseous solutions—which are more commonly regarded simply as mixtures—are used... 

FIGURE 21.11 MO energy levels for doped semiconductors, (a) An M-type semiconductor, such as silicon doped with phosphorus, has more electrons than needed for bonding and thus has negative electrons in the partially filled conduction band. 

As an example of the use of this technique, a silicon wafer lightly doped with phosphorus is doped with additional phosphorus by ion implantation (dose of 3.5 x 10ncm"2). A thermal oxide film of 857 A thickness was initially grown on the wafer. The variation of dopant concentration with depth from the oxide-silicon interface is shown in Figure 16. The rise in dopant close... 

The silicon materials that are used in the electronic industry are normally doped to increase the conductivity. The common donors for silicon are P, As, and Sb and the acceptors are B, Al, and Ga. They are substitutional impurities with ionization levels located in the range of 0.04 to O.OVeV from the corresponding bands. Table 2.2 lists the resistivity, which is the reciprocal of the conductivity, of n- and p-type silicon doped with phosphorus and boron, respectively. ... 

Describe the nature of electrical conduction in (a) silicon doped with phosphorus and (b) indium antimonide doped with zinc. 

An n-type semiconductor contains an excess of electrons from the point of view of bonding but not, of course, from the point of view of nuclei in terms of charge, the extra electrons in silicon doped with phosphorus are balanced by the extra positive charge on the phosphorus nuclei. It is important to remember that n-type semiconductors are electrically neutral. There is no net charge on silicon doped with phosphorus, for example, because it is composed of neutral atoms. 

Orbital energy-level diagram for an impurity semiconductor silicon doped with phosphorus. 

Figure 4. A schematic representation of the metal-insulator transition in (a) Si P (the semiconductor silicon doped with phosphorus) and (b) a divided metal. The expected behavior of the d.c. conductivity at T = 0 K is shown. In Si P (a) a first-order transition is sketched. For the divided metal (b), both first-order and continuous transitions are shown. Modified from Edwards. ...

Calculate the donor energy-level position in silicon doped with phosphorus using the Bohr model . The effective mass of an electron is 0.33me and the relative permittivity of silicon is 11.7. 

To avoid catalytic interaction of the analyte with a heater made of noble metal, the films are frequently coated with a thin, chemically inert layer of SiO. Such passivation very often serves as a support for further functional layers in top-down microelectronic technologies. It should be noted that the passivation of electrode materials allows a reduction in requirements relating to their thermodynamic stability. In particular, the indicated approach is used in micro-hotplate fabrication. As a result most micro-hotplate designers consider polycrystalline silicon doped with boron or phosphorus impurities to be a very appropriate material for making heaters and temperature sensors because, with capsulation covering, it is stable up to 1,000 °C (Panchapakesan et al. 2001 Hwang... 

A) Silicon doped with phosphorus.The extra electrons (denoted e ) from phosphorus atoms are free to conduct a current. (6) Silicon doped with boron. A bond with a missing electron Is equivalent to a positively charged hole, indicated here as a plus sign In a circle. 

Hyperpure silicon can be doped with boron, gallium, phosphorus, or arsenic to produce silicon for use in transistors, solar cells, rectifiers, and other solid-state devices which are used extensively in the electronics and space-age industries. 

Silicon can be doped with small amounts of phosphorus to create a semiconductor used in transistors, (a) Is the alloy interstitial or substitutional Justify your answer, (b) How do you expect the properties of the doped material to differ from those of pure silicon ... 

As an alternative to QDs, silicon can be doped with single atom impurities, in particular phosphorus, which acts as an electron donor. Donors can be implanted individually with a precision of about 10 nm. Either the 31P nuclear spin or the unpaired electron can be used as qubits [63, 64]. An advantage of silicon is its widespread use in current electronics, meaning that QC might profit from methods and technologies already developed for their classical cousins . Also, spins in silicon can attain extremely high coherence times experiments on 28 Si-enriched silicon show spin coherence times T2 exceeding 10 s [65]. The read-out and coherent manipulation of individual spin qubits in silicon have been recently achieved [66]. 

Fig. 20. SIMS profiles of total deuterium density across p-n junctions formed by implanting phosphorus into a (100) silicon water uniformly doped with 1 x 1017 boron atoms per cm3 for various times of deuteration at 150°C (Johnson, 1986a). The phosphorus profile is also shown and serves to locate the pre-deuteration depth of the junction at 0.5 Deuteration was from downstream gases from a plasma discharge (Johnson and Moyer, 1985).

Fig. 31. SIMS plots of total deuterium density for n-type silicon specimens with various donor concentrations, deuterated by plasma gases at 300°C. Full curves are from recent measurements with one hour deuteration (Johnson, 1989) dashed curves are older data with two hour deuteration (Johnson, 1987). The donor for both these sets was phosphorus. The dotted curve shows data for one hour deuteration of a wafer with antimony doping. Each curve is labeled with its donor concentration in atoms/cm3. All sample surfaces were prepared in the same manner as those of Fig. 29. 

Chapter 4 discussed semiconductivity in terms of band theory. An intrinsic semiconductor has an empty conduction band lying close above the filled valence band. Electrons can be promoted into this conduction band by heating, leaving positive holes in the valence band the current is carried by both the electrons in the conduction band and by the positive holes in the valence band. Semiconductors, such as silicon, can also be doped with impurities to enhance their conductivity. For instance, if a small amount of phosphorus is incorporated into the lattice the extra electrons form impurity levels near the empty conduction band and are easily excited into it. The current is now carried by the electrons in the conduction band and the semiconductor is known as fl-type n for negative). Correspondingly, doping with Ga increases the conductivity by creating positive holes in the valence band and such semiconductors are called / -type (p for positive). 

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. 

Silicon dioxide films have been an essential factor in the manufacture of integrated circuits from the earliest days of the industry. They have been used as a final passivation film to protect against scratches and to getter mobile ion impurities (when doped with phosphorus). Another application has been as an interlayer dielectric between the gate polysilicon and the aluminum metal-ization. Initially, most such films were deposited in atmospheric pressure systems. In recent years, low pressure processes have assumed greater importance. We will begin by examining the atmospheric process. 

Earlier, we reviewed silicon dioxide (thermal) films deposited with added phosphorus to serve as a getter for mobile ion impurities, as a final passivation film. Plasma-enhanced silicon nitride can also be doped with phosphorus.6 Some of the film characteristics have been reviewed, and it was found that the films with 2 to 3% P had the best electrical quality. No measurements of stress or H2 content were reported, so it is not clear that these would be use-able films. 

Semiconductors may also be made from a material which is normally an insulator by introducing an impurity, a process known as doping. Figure 9.9 shows two ways in which an impurity may promote semiconducting properties. In Figure 9.9(a) the dopant has one more valence electron per atom than the host and contributes a band of filled impurity levels I close to the conduction band of the host. This characterizes an n-type semiconductor. An example is silicon (KL3s23p2) doped with phosphorus KL3s13pi), which reduces the band gap to about 0.05 eV Since kT at room temperature is about 0.025 cV, the phosphorus... 

The thermodynamics of doped a-Si H is a little more complicated, because both the defects and dopants are charged and so interact with the electron distribution whose chemical potential is the Fermi energy. The analysis is for the specific case of n-type doping with phosphorus and, following the model introduced in Chapter 5, it is assumed that both the phosphorus and sUicon atoms may have either three-fold or four-fold coordination. The ground state configuration comprises the four-fold silicon and the three-fold phosphorus, and the defect reaction is,... 

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