N-TYPE PREFERRED IN OPTICS

N-TYPE AND P-TYPE IN OPTICS

N-type and p-type starting material (Si feedstock), have the same type of silicon crystals. However, the doping process during crystallization is the difference with n-type using a phosphorus doping process and p-type a boron process.

There has been a lot of scientific research within the past 10 years on phosphorus doped n-type silicon (Si) material. Compared to the standard p-type boron doped Si material, n-type silicon has two important advantages.

1. N-type Si material does not degrade with light induced presence of boron and oxygen wafers as p-type does, which leads to a reduction of module power output by usually three percent within the first week of use.

2. N-type Si material is less sensitive to impurities usually present in silicon feedstock, which leads to assurances that Si material, n-type, does not have to be procured with high electronic quality. Hence, n-type Si material can be produced more cost effectively than high quality p-type.

The Czochralski (CzSi) pulling method has been shown to produce a very high quality monocrystalline, high diffusion length of charge carriers, without suffering from LID (light induced degradation). The n-type Si material shows a larger distribution of specific electrical resistance at 3 to 12 Ωcm compared to p-type at 1 to 3 Ωcm.

METHOD FOR DETERMINING OPTIMAL MATERIAL IN OPTICS

Using a spectroscopic device in the range of 0.1 to 2.0THz (see figure 1), the optoelectronic generation and reception of a beam’s sub-picosecond THz pulses, is able to conclude with the shapes of the pulses, the absorption and dispersion. The n- and p- type samples were measured at equivalent resistance levels with a (111) orientation.

FIGURE 1

With the dopants directly affecting the charge carrier characteristic, the frequency-dependent properties appear to be due to the wafer dopant material and not the crystal formation. The n-type Si material was measured to be 1.7% higher of cold initial resistance value while the p-type was 3.4% above.

For more information about n-type silicon material, contact Applied Watts today.