Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

5.6 Realization of P-N Junction Structure
5.6 Realization of P-N Junction Structure
Another task is to realize a P-N structure by MBE. The capability of realizing
well-controlled abrupt doping proles and alloy heterojunctions oer many opportunities
to implement device structures, however, have not been practical or
realizable by MBE in silicon in the past. The development of Si MBE technology
is particularly important since there is an enormous Si technology base already
existing in industry, and any new advance in Si technology is extremely important
to the semiconductor industry as a whole. However, in order to realize P-N junction
structure as well as controlled doping prole for light emitting diode (LED)
applications, a Si layer with dierent As 4 uxes and dierent Si thicknesses was
grown on exactly oriented undoped Si (100) substrate in MBE system. Group V
semiconductors like arsenic (As) or phosphor (P) act as n-type dopant of Si. The
silicon homoepitaxial growth was performed by electron beam evaporation system
(EBE), since the vapor pressure of silicon is extremely low, and conventional
eusion cells cannot generate a sucient silicon vapor. However, due to the fact
that in our III-V MBE system used for silicon homoepitaxy only an arsenic cell
is installed and no phosphorous cell, the n-type doping in Si was performed by
As 4 .
After our standard ex-situ (BHF wet etching for 2 min.) and in-situ (thermal
oxide desorption at 870 ◦ C for 15 min.) surface treatment, the substrate temperature
was reduced to 650 ◦ C for doped Si layer growth. The growth rate of
Si was set to ∼ 5 nm/min, which corresponds to an emission current of 68 mA
and voltage of 6 kV. However, in order to study the inuence of As 4 ux on the
doping level of the grown Si layer, three dierent samples with dierent As 4 uxes
were grown with the same growth conditions and same Si layer thickness. A Si
buer layer with 100 nm thickness was grown at 650 ◦ C and As 4 equivalent beam
pressure (EBP) of 1.2 × 10 −8 Torr. While, the next two samples were grown as
the rst sample but with double and triple As 4 ux. After that, a contact layer of
metallic contact stripes with 20 nm Pt, 80 nm Ti and 300 nm Au were deposited
on the top of the doped Si layer for further electrical resistivity characterizations
as shown in Fig. 5.31. The red arrow shows the direction of the current ow
between two of the stripes highlighted in dark-orange color. The measurement
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