Variational Calculations of Donor Binding Energy in Rectangular Wurtzite Aluminium Gallium Nitride / Gallium Nitride Qua
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1040-Q02-04
Variational Calculations of Donor Binding Energy in Rectangular Wurtzite Aluminium Gallium Nitride / Gallium Nitride Quantum Wires Choudhury Jayant Praharaj Electrical and Computer Engineering, Cornell University, Ithaca, NY, 14853 ABSTRACT We present variational calculations of donor binding energy in rectangular wurtzite aluminium gallium nitride / gallium nitride quantum wires. We explicitly take into account the effect of spontaneous and piezoelectric polarization on the energy levels of donors in quantum wires. Wurtzite structure nitride semiconductors have spontaneous polarization even in the absence of externally applied electric fields. They also have large piezoelectric polarization when grown as pseudomorphic layers. The magnitude of both polarization components is of the order of 1013 electrons per cm2 , and has a non-trivial effect on the potential profile seen by electrons. Due to the large built-in electric fields resulting from the polarization discontinuities at heterojunctions, the binding energies of donors is a strong function of the position inside the quantum wire. The potential profile in the 0001 direction can vary by as much as 1.5eV due to polarization effects for vertical dimensions of the quantum wire up to 20 angstroms. The probability density of electrons tends to concentrate near the minimum of the conduction band profile in the 0001 direction. Donors located close to this minimum tend to have a larger concentration of electron density compared to those located closer to the maximum. As a consequence, the binding energy of the former are higher compared to the latter. We use Gaussian variational wavefunctions to calculate the binding energy as a function of donor position. The confinement potential enhances the binding by a factor of about 3 compared to donors in bulk nitride semiconductors, from about 30 meV to about 90 meV. The variation of binding energy with position is calculated to be more than 50% for typical compositions of the quantum wire regions. Our calculations will be useful for understanding device applications involving n-doped nitride quantum wires. INTRODUCTION Wide band-gap semiconductors belonging to the group III nitride series have attracted considerable attention in recent years due to a combination of desirable material properties like low impact ionization coefficients, high breakdown fields and accessibility to the blue and ultraviolet part of the radiation spectrum. Low-dimensional structures in these semiconductors have been the focus of a large number of research papers due to the ability to manipulate electron and hole transport to meet device requirements that cannot be met by lower band-gap semiconductors. As the dimensions of devices decreases, several properties, including binding energies of acceptors and donors, become modified by confinement in one or more directions. We present theoretical calculations of donor binding energy in rectangular quantum wires of gallium nitride with aluminium gallium nitride providing the confinement potenti
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