Strained M -plane GaN for the realization of polarization-sensitive photodetectors

Self Cite

We have used polarized photoreflectance (PR) spectroscopy to study [1120]-oriented A-plane GaN films on R-plane sapphire substrates. For this type of films, the c-axis of GaN lies in the film plane. When the probe beam is polarized perpendicular to the c-axis, we observe a single feature in the PR spectrum, while two features at higher energies are observed for parallel polarization. Comparing the transition energies with the ones obtained by electronic band-structure calculations, we identify the observed PR spectral features as the three possible transitions around the fundamental band gap of GaN. However in comparison to unstrained GaN, their polarization properties and energies have been significantly modified by the inplane anisotropic strain in the film. Finally, we can also determine the individual in-plane anisotropic strain components.

Section: Resultscontrasting

confidence: 63%

Section: Resultsmentioning

confidence: 87%

Optical polarization anisotropy in strained A‐plane GaN films on R‐plane sapphire

Ghosh

Misra

Grahn

et al. 2006

Self Cite

“…The third uppermost VB is not involved in the absorption process for light polarized in the M plane, since the corresponding transition 3 T with the CB is polarized perpendicular to the plane of incidence, i.e., the y-direction [11]. This type of in-plane polarization anisotropy may be very useful for the realization of polarization-sensitive photodetectors [14].…”

Section: Introductionmentioning

confidence: 98%

Polarization properties of nonpolar GaN films and (In,Ga)N/GaN multiple quantum wells

Grahn

2004

Self Cite

We have realized nonpolar GaN films and (In,Ga)N/GaN multiple quantum wells (MQWs) by plasmaassisted molecular-beam epitaxy on γ-LiAlO 2 (100) substrates. The GaN films and (In,Ga)N/GaN MQWs are grown in an M-plane configuration, i.e., the c-axis of the wurtzite unit cell lies in the growth plane. For compressively and anisotropically strained M-plane GaN films, the band structure of the valence band changes in such a way that the optical transmittance becomes 100% linearly polarized for two orthogonal in-plane directions, where one of these directions is parallel to the c-axis of the GaN film. Within a certain energy range, the M-plane GaN film thereby acts as a polarization filter. The photoluminescence spectra of M-plane In 0.1 Ga 0.9 N/GaN MQWs exhibit a strong in-plane optical anisotropy for linear polarization with an energy-dependent polarization degree of up to 96%, which is presumably also due to a large valence-band splitting induced by the large compressive strain in the QWs.

“…The third upper-most valence band is not involved in the absorption process for light polarized in the M plane, since the corresponding transition T 3 with the conduction band is polarized perpendicular to the plane of incidence, i.e., the y-direction. This type of in-plane polarization anisotropy may be very useful for the realization of polarization-sensitive photodetectors [10].…”

mentioning

confidence: 99%

Angular dependence of the in‐plane polarization anisotropy in the absorption coefficient of strained M‐plane GaN films on γ‐LiAlO₂

Misra

Sun

Brandt

et al. 2003

Self Cite

We investigate the in-plane polarization properties of GaN films grown by plasma-assisted molecularbeam epitaxy on LiAlO 2 (100). Due to the crystal symmetry of LiAlO 2 (100), GaN films can be realized in a nonpolar (M-plane) configuration, i.e., the c-axis of the wurtzite unit cell lies in the growth plane. For strained M-plane GaN films, the band structure of the valence band changes in such a way that the optical transmittance is completely linearly polarized for two orthogonal in-plane directions, where one of these directions is parallel to the c-axis of the GaN film. The transmittance for an arbitrary in-plane polarization angle can be described as a linear combination of the transmittance for two orthogonal polarization, one of which is parallel to the c-axis.1 Introduction The internal quantum efficiency of GaN-based light-emitting devices is still not optimized due to the presence of electrostatic fields within the active layer, which usually consists of a heterostructure such as a quantum well. These electrostatic fields are generated by the spontaneous and piezoelectric polarization along the ½0001 axis of the hexagonal group-III nitrides. The film growth direction is usually along ½0001, i.e., C-plane films, so that these electrostatic fields will separate the electron and hole wave-functions in quantum well structures. The resulting reduction in the wave-function overlap decreases the radiative efficiency for light-emitting devices. A way to overcome this problem is to realize quantum-well structures with the c-axis of the wurtzite unit cell being in the growth plane in order to achieve a nonpolar direction, e.g. Second, for in-plane strain values smaller than À0:2%, which are typical for our films, the valence band structure is changed in such a way that the transition T 1 between the uppermost valence band and the conduction band becomes completely linearly polarized in the x-direction, while the transition T 2 of the second uppermost valence band with the conduction band is completely linearly polarized in the z-direction, which is parallel to the c-axis of the film. The third upper-