Optoelectronic Semiconductor Devices Principals and Characteristics

2.2.1 
III-V SEMICONDUCTOR

They consist of the elements from columns III and V of the periodic table, (Table 

2.
) and of the form of 
A
x
B
1-x
C, where x- the mole fraction in range from 0 to 1.

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Table 2.: Periodic Table. 
These III-V compounds have emerged as the materials of choice for lasers that emit in the 0.7-1.6 µm 
wavelength range. This range includes the important fiber-optic communication bands at 0.85, 1.31 and 
1.55 µm, the pumping bands for fiber amplifiers at 1.48 and 0.98 µm, the the window for pumping Nd-
doped YAG (yttrium-aluminum-garnet) at 0.81 µm and the wavelength currently used for optical disk 
players at 0.78 µm. 
Most of these materials have a direct gap in E-k space, which means that the minimum and maximum of 
the conduction and valence bands, respectively, fall at the same k-value. (Figure 
3.
). 
Figure 3.: Photon emission in direct and indirect band-gap semiconductors.
[1]

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Since there are three group III atoms (Al, Ga and In) and three group V atoms (P, As and Sb), there are 18 
possible ternary III-V solutions. 
Some of the III-V solid solutions have direct band-gap and others have indirect. This means that not all 
ternary semiconductors are good optical materials. 
With quite a good precision, the lattice constant of quaternaries can be calculated from Vegard's law, 
which gives a value equal to the weighted average of all of the four possible constituent binaries. For 
example, in In
1-x
Ga
x
As
y
P
1-y
, we obtain
(2) 
( , )
(1
)
(1
)
(1
)(1
)
GaAs
GaP
InAs
InP
a x y
xya
x
y a
x ya
x
y a
=
+
−
+ −
+ −
−
Similarly, the lattice constant for other alloys can be calculated using Formula (2). 
In addition to the usual III-V compounds, Table 
3.
also lists some of the nitride compounds. These have 
gained an attention because of a success in demonstrating LEDs emitting at high energies in the visible 
spectrum.