Taking the strong built-in electric field into account

the optical-rectification (OR) coefficient in a nitride semiconductor coupling quantum well (CQW) has been theoretically investigated by using the compact density matrix approach in the present paper. In general

in order to obtain strong even-order optical nonlinea-rities

one should constitute a quantum confined systems with asymmetrical potential profile

such as compositionally asymmetric quantum well (QW)

and applied-field-based QW. It is well known that there exists very strong built-in electric field in GaN-based heterostructure due to the strong spontaneous macroscopic polarization and large piezoelectric coefficients. For the commonly used [0001]-oriented InGaN/GaN strained QW

the magnitude of the built-in electric field is estimated to be in the order of MV/cm. The built-in electric field with order of MV/cm can naturally break the inversion symmetry of the nitride quantum confined potential profile. Hence a very large even-order optical nonlinear susceptibility can be expected in such systems. Based on the built-in electric field model already constituted in recent reference

the electronic eigenstates in a nitride CQW are exactly solved. Numerical calculation on a typical GaN/In

x

Ga

1-x

N CQW was performed. The calculated results reveal that the resonant OR coefficient achieves the magnitude of 10

-6

m/V

and the dipole matrix elements of the systems also reach more than 2nm

which is apparently larger than the corresponding values in single wurtzite quantum wells. Moreover

we find that the OR coefficients of the CQW are not monotonic functions of the well width

barrier width and the doped concentration of the CQW systems

but have complicated dependent relations on them. The reason resulting in this characteristic is mainly attributed to the intense competition between the strong built-in electric field effect and the quantum size effect for the carrier in the wurtzite CQW systems. Our calculation also shows that a strong OR effect can be realized in the nitride CQW by choosing optimized structural parameters and relatively low doped fraction.