Boron silicon doped 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. 

The ability of atomic hydrogen to neutralize acceptors other than boron is demonstrated in Fig. 10. Samples of silicon doped with Al, Ga, and In were exposed to Hx at 125°C for one hour. They all exhibit an increase in spreading resistance at the surface by at least one order of magnitude. 

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. ... 

Like the n-type semiconductors, silicon doped with boron is composed of neutral atoms and is uncharged. For each boron atom in the crystal there will be one electron fewer in the highest filled band of silicon. Because the valence band is now only partly full, boron-doped silicon is a better conductor than pure silicon. The current in p-type semiconductors is carried by the few mobile electrons in the valence band, and is proportional to the number of empty levels in this band. 

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... 

Sihcon metal of the highest degree of purity is used in solar cells, a new ecofriendly energy source. Sunlight can be converted to electricity in thin-fihn photovoltaic modules of sihcon deposited on titanium dioxide. Another method is to use a wafer, composed of a layer of silicon doped with arsenic (an n-type semiconductor) combined with a layer doped with boron (a p-type semiconductor). When exposed to sunhght electrons flow between the p- and n-layers and thus an electric current is generated. 

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. 

In the boldest approach so far, we are trying to build an all-silicon trap (Figure 4). The conductive electrodes are made of silicon doped with boron ... 

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. 

Fig. 17. Advance of a passivated region into silicon uniformly doped with 5 x 1018 boron atoms per cm3, after exposure for 30 min. at about 150°C to atomic deuterium from a plasma source (Johnson, 1985a). (a) Spreading resistance profile, (b) Depth distribution of total deuterium and of boron from SIMS.

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).

Figure 4.22 Schematic diagram of a field effect transistor. The silicon-silicon dioxide system exhibits good semiconductor characteristics for use in FETs. The free charge carrier concentration, and hence the conductivity, of silicon can be increased by doping with impurities such as boron. This results in p-type silicon, the p describing the presence of excess positive mobile charges present. Silicon can also be doped with other impurities to form n-type silicon with an excess of negative mobile charges.

DC Conduction. Cross-sectional and top views of the test structures for the dc conduction measurements are shown in Figure 1. Fabrication begins with p-type silicon wafers 3 inches in diameter, which are first doped with boron on the front... 

The properties of semiconductors are extremely sensitive to the presence of impurities at concentrations as low as 1 part in 10 °. For this reason, silicon manufactured for transistors and other devices must be very pure. The deliberate introduction of a very low concentration of certain impurities into the very pure semiconductor, however, alters the properties in a way that has proved invaluable in constructing semiconductor devices. Such semiconductors are known as doped or extrinsic semiconductors. Consider a crystal of silicon containing boron as an impurity. Boron has one fewer valence electron than silicon. Therefore, for every silicon replaced by boron, there is an electron missing from the valence band (Figure 4.10) (i.e., positive holes occur in the valence band and these enable electrons near the top of the band to conduct electricity). Therefore, the doped solid will be a better conductor than pure silicon. A semiconductor like this doped with an element with fewer valence electrons than the bulk of the material is called a p type semiconductor because its conductivity is related to the number of positive holes (or empty electronic energy levels) produced by the impurity. 

When a silicon ciystal is doped with atoms of elements having a valence of less than four, e.g., boron or gallium (valence =3), only three of the four covalent bonds of the adjacent silicon atoms are occupied. The vacancy at an unoccupied covalent bond constitutes a hole. Dopants that contribute holes, which in turn act like positive charge earners, are acceptor dopants and the resulting crystal is p-type (positive) silicon. See Fig. 1(d). 

A p-type (for positive type) semiconductor is an electron poor material comprised of silicon (a Group IV element) doped with something like boron (Group III). Boron atoms have one less valence electron than silicon atoms, so the crystalline lattice has fewer electrons—or more positive holes —in it compared to pure silicon. This is illustrated in Figure 10.13. 

---