Polarization filtering by nonpolar M-plane GaN films on LiAlO2

Misra, P.; Sun, Yue; Brandt, O.; Grahn, H. T.

doi:10.1063/1.1808483

Cited by 28 publications

(15 citation statements)

References 39 publications

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“…Besides, the in-plane crystal symmetry can be further reduced by the effect of in-plane anisotropic strain generated by the lattice mismatch between the GaN and the substrate. In particular, the valence band structure of M-plane GaN grown on LiAlO 2 substrates is modified in such a way that the topmost transitions become purely polarized either perpendicular (E ⊥ c) or parallel (E || c) to the c-axis [9,10,81,82]. These properties have been used to fabricate SB as well as MIS polarization-sensitive UV photodetectors [10].…”

Section: Polarization Sensitive Photodetectorsmentioning

confidence: 98%

(Al,In,Ga)N‐based photodetectors. Some materials issues

Muñoz

2007

Physica Status Solidi (b)

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www.pss-b.com filters are needed to stop low energy photons (VIS and infrared light), degradation is produced by UV photons (shorter device lifetime), efficiency lowers, dark current increases markedly with temperature, etc. The development of higher band gap III-arsenides or III-phosphides for UV photodetection did not progress substantially. On the other hand, for high sensitivity UV applications, PMT are needed, being bulky and requering a high-voltage power supply [1][2][3].To avoid the use of filters, to increase efficiency, to lower noise and dark current specially above room temperature, and to achieve visible-blind operation, UV detectors based on wide band gap semiconductors have been studied during the last decade. Thin film synthetic diamond detectors (E g = 5.4 eV, 227 nm, direct gap), were developed and commercialised mainly as polycrystalline photoconductor devices. SiC p-n junction PD (4H-SiC, E g = 3.26 eV; 6H-SiC, E g = 3 eV, indirect gap), have been also available. However, the turning point to make visible-blind UV detectors an appealing reality, to open really new possibilities for UV detection, has been the development of (Al,In,Ga)N semiconductors. The possibility of selecting the cut-off wavelength by adjusting the mole fraction of the ternary or quaternary alloys is unique, so far not being proven by any other wide-band-gap semiconductor family [2].III-nitrides are direct band gap materials, with GaN showing its absorption edge at 360 nm (E g = 3.44 eV) and at 200 nm for AlN (E g = 6.2 eV), and with the ability to form heterojunctions and to withstand high temperatures. Even the 400 nm UV frontier can be reached using (In,Ga)N alloys (band gap assigned today to InN is 0.7 eV). This tunability of the detection edge by just varying the Al(In) mole fraction, and the fact that (Al,In,Ga)N technology is already fully commercial for light emitting diodes, laser diodes (LEDs and LDs, respectively) [4], and it has just started for high electron mobility transistors (HEMTs), are very important points that have made (Al,In,Ga)N alloys the most adequate solution for UV detection in many applications. Besides, the high chemical and thermal stability of GaN, GaN-based detectors are also of interest for high photon energy detection (e.g. VUV and X-rays) and even for high energy particle detection [5].The photoconductive properties of GaN were studied by Pankove and Berkeyheiser in 1974 [6], and in about fifteen years of III-nitrides technology, the first GaN UV photoconductive detectors were reported by Khan in 1992 [7]. Since then, practically all types of PD structures have been developed, directly linked to advances in GaN and AlGaN epitaxial growth, and to progresses in p-type doping and in ohmic and Schottky contact technology. Trying to give a perspective of the developments, we may consider an initial exploratory phase (a proof of concept, first generation of UV detectors, VIS blind), just trying to confirm that GaN and AlGaN PDs (with low-medium Al mole fractions) were feasible. Later, a second ...

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Section: Polarization Sensitive Photodetectorsmentioning

confidence: 98%

(Al,In,Ga)N‐based photodetectors. Some materials issues

Muñoz

2007

Physica Status Solidi (b)

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“…The details of the extraction of these values are reported in Ref. [10]. Note that the dichroism ∆α becomes maximal between 3.4 and 3.5 eV, where the birefringence ∆n almost vanishes.…”

Section: Polarization Anisotropy In Transmission Spectramentioning

confidence: 96%

Polarization anisotropy and filtering for M ‐plane GaN films

Misra

Sun

Brandt

et al. 2005

phys. stat. sol. (c)

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PACS 42.25.Ja, 78.20.Ek, 78.20.Fm, 78.66.Fd The polarization anisotropy and filtering are investigated for strained M-plane GaN films as a function of the angle of the in-plane polarization vector. In addition to linear birefringence, the film also exhibits linear dichroism, resulting in a polarization filtering of an incident, linearly polarized light beam after transmission. This filtering manifests itself as a rotation of the polarization vector toward the c axis, which can be as large as 75• . In the energy range where the filtering is most effective, the birefringence almost disappears and can therefore be neglected for the determination of the rotation angle. Consequently, the rotation can be very well approximated by the product of the film thickness and the difference of the absorption coefficients for the two polarization directions. Temperature-and polarization-dependent photoluminescence (PL) spectroscopy was also used to study the polarization anisotropy. For an arbitrary initial polarization angle, the total PL intensity can be decomposed into two contributions due to the PL intensity for E c and E ⊥ c.1 Introduction For C-plane GaN films, the growth is along the [0001] direction, which is parallel to the c axis of the wurtzite (WZ) crystal structure. While isotropic strain in the C plane preserves the crystal symmetry in the x-y plane, anisotropic strain can result in an in-plane polarization anisotropy [1]. For M-plane GaN films, the growth direction is along [1100] so that the c axis lies in the growth plane. Therefore, an in-plane polarization anisotropy will occur even in the absence of in-plane strain [2]. Furthermore, anisotropic in-plane strain can drastically enhance the in-plane polarization anisotropy. For a certain range of in-plane strain values, the valence-band (VB) structure changes in such a way that the transitions between the three uppermost VBs and the conduction band labelled T 1 , T 2 , and T 3 become fully polarized in the x-, z-, and y-direction, respectively [3,4].In this paper, we present a theoretical and experimental investigation of the in-plane optical polarization properties of M-plane GaN films grown on γ-LiAlO 2 (100). In addition to linear birefringence, the film also exhibits linear dichroism, resulting in a very effective polarization filtering. We have included both effects to describe this polarization filtering, which can be detected as a rotation of the in-plane polarization vector. The rotation angle can be approximately described by the film thickness times the difference in the absorption coefficients for the two polarization directions. Although the outgoing light is generally elliptically polarized, it turns out that, in the energy range where the polarization filtering is most effective, the linear birefringence almost vanishes. As mentioned above, the polarization filtering is a manifestation of the modified VB structure, and the energy separation between the two uppermost VB's corresponding to the transitions T 1 and T 2 becomes more than 40 meV at 3...

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“…5(a)]. At the maximum of the polarization filtering around 360 nm, the birefringence of the film can be neglected [23]. The squares in Fig.…”

Section: Static and Dynamic Polarization Filteringmentioning

confidence: 99%

Optical polarization anisotropies in GaN films for different nonpolar orientations

Grahn

2007

Physica Status Solidi (b)

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We have used polarized photoreflectance spectroscopy to study the electronic-band-structure modification of GaN films grown along different nonpolar orientations due to biaxial, anisotropic in-plane strain. For nonpolar oriented films, the c-axis of GaN lies in the film plane. In four different GaN films with a nonpolar orientation (M-and A-plane), we observe a large in-plane optical polarization anisotropy, which is much larger for the M-plane films due to the much larger strain in at least one of the in-plane directions. The experimental results for the transition energies and oscillator strengths are compared with theoretical results obtained using the k ⋅ p perturbation approach. The large optical polarization anisotropy in M-plane GaN films can be used for polarization filtering and polarization-sensitive photodetectors.

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Polarization filtering by nonpolar M-plane GaN films on LiAlO2

Cited by 28 publications

References 39 publications

(Al,In,Ga)N‐based photodetectors. Some materials issues

(Al,In,Ga)N‐based photodetectors. Some materials issues

Polarization anisotropy and filtering for M ‐plane GaN films

Optical polarization anisotropies in GaN films for different nonpolar orientations

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