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1.
Sci Rep ; 9(1): 3243, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30824803

RESUMO

In this study, the blue light-emitting diode (LED) structures based on gallium nitride (GaN) were presented. Each structure possessed a surface GaN p-n junction, which was formed through selective area regrowth on an InGaN/GaN multiple quantum well (MQW) structure and served as the carrier injector. The LEDs that showed efficient hole injection and current spreading were configured to form a p-type GaN layer between the MQW and regrown n-type GaN top layer. These LEDs exhibited higher luminous efficiency and lower operation voltage than the LEDs with regrown p-type GaN top layers. The LEDs with n-type GaN top layers emitted single-peak spectra at approximately 450 nm under a forward bias. The UV peak at 365 nm (i.e., the GaN band-edge emission) was absent because the regrown surface GaN p-n junctions behaved as carrier injectors rather than photon injectors. In other words, the single-peak blue emission was not generated by the optical pumping of UV light emitted from the surface p-n GaN homojunction.

2.
Sci Rep ; 8(1): 8641, 2018 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-29872117

RESUMO

The effect of Mn concentration on the optical properties of Mn-doped layers grown by metalorganic vapor phase epitaxy is investigated. The Mn-doped GaN layers exhibite a typical transmittance spectrum with a distinct dip around 820 nm which is attributed to the transition of electrons between the edge of valence band and the Mn-related states within the bandgap. In addition, electroluminescence (EL) spectra obtained from the bipolar devices with Mn-doped GaN active layer also show that considerable Mn-related energy states existed in the bandgap. The position of the Mn-related energy states in the GaN is first evaluated via EL spectra. In addition to the absorption of band edge, the Mn-related energy states behaving like an intermediate band cause an additional sub-band gap absorption. Consequently, the fabricated GaN-based solar cells using Mn-doed GaN as the absorption layer exhibit photocurrent higher than the control devices without Mn doping. Under one-sun air mass 1.5 G testing condition, the short-circuit current of the Mn-doed GaN solar cells can be enhanced by a magnitude of 10 times compared with the cells without Mn doping.

3.
Opt Express ; 25(16): A777-A784, 2017 Aug 07.
Artigo em Inglês | MEDLINE | ID: mdl-29041045

RESUMO

Monolithic stacked InGaN light-emitting diode (LED) connected by a polarization-enhanced GaN/AlN-based tunnel junction is demonstrated experimentally in this study. The typical stacked LEDs exhibit 80% enhancement in output power compared with conventional single LEDs because of the repeated use of electrons and holes for photon generation. The typical operation voltage of stacked LEDs is higher than twice the operation voltage of single LEDs. This high operation voltage can be attributed to the non-optimal tunneling junction in stacked LEDs. In addition to the analyses of experimental results, theoretical analysis of different schemes of tunnel junctions, including diagrams of energy bands, diagrams of electric fields, and current-voltage relation curves, are investigated using numerical simulation. The results shown in this paper demonstrate the feasibility in developing cost-effective and highly efficient tunnel-junction LEDs.

4.
Opt Express ; 23(7): A232-9, 2015 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-25968789

RESUMO

We present a trichromatic GaN-based light-emitting diode (LED) that emits near-ultraviolet (n-UV) blue and green peaks combined with red phosphor to generate white light with a low correlated color temperature (CCT) and high color rendering index (CRI). The LED structure, blue and green unipolar InGaN/GaN multiple quantum wells (MQWs) stacked with a top p-i-n structure containing an InGaN/GaN MQW emitting n-UV light, was grown epitaxially on a single substrate. The trichromatic LED chips feature a vertical conduction structure on a silicon substrate fabricated through wafer bonding and laser lift-off techniques. The blue and green InGaN/GaN MQWs were pumped with n-UV light to re-emit low-energy photons when the LEDs were electrically driven with a forward current. The emission spectrum included three peaks at approximately 405, 468, and 537 nm. Furthermore, the trichromatic LED chips were combined with red phosphor to generate white light with a CCT and CRI of approximately 2900 and 92, respectively.

5.
Opt Express ; 23(7): A371-81, 2015 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-25968802

RESUMO

A p-i-n structure with near-UV(n-UV) emitting InGaN/GaN multiple quantum well(MQW) structure stacked on a green unipolar InGaN/GaN MQW was epitaxially grown at the same sapphire substrate. Photon recycling green light-emitting diodes(LEDs) with vertical-conduction feature on silicon substrates were then fabricated by wafer bonding and laser lift-off techniques. The green InGaN/GaN QWs were pumped with n-UV light to reemit low-energy photons when the LEDs were electrically driven with a forward current. Efficiency droop is potentially insignificant compared with the direct green LEDs due to the increase of effective volume of active layer in the optically pumped green LEDs, i.e., light emitting no longer limited in the QWs nearest to the p-type region to cause severe Auger recombination and carrier overflow losses.

6.
Opt Express ; 23(7): A401-12, 2015 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-25968805

RESUMO

Non-planar InGaN/GaN multiple quantum well (MQW) structures are grown on a GaN template with truncated hexagonal pyramids (THPs) featuring c-plane and r-plane surfaces. The THP array is formed by the regrowth of the GaN layer on a selective-area Si-implanted GaN template. Transmission electron microscopy shows that the InGaN/GaN epitaxial layers regrown on the THPs exhibit different growth rates and indium compositions of the InGaN layer between the c-plane and r-plane surfaces. Consequently, InGaN/GaN MQW light-emitting diodes grown on the GaN THP array emit multiple wavelengths approaching near white light.

7.
Nanoscale Res Lett ; 9(1): 596, 2014.
Artigo em Inglês | MEDLINE | ID: mdl-25392706

RESUMO

This paper aims to investigate the light output power (LOP) of InGaN-based light-emitting diodes (LEDs) grown on patterned sapphire substrates (PSSs) with different symmetry. The GaN epitaxial layers grown on the hexagonal lattice arrangement PSS (HLAPSS) have a lower compressive strain than the ones grown on the square lattice arrangement PSS (SLAPSS). The quantum-confined Stark effect (QCSE) is also affected by the residual compressive strain. Based on the experimentally measured data and the ray tracing simulation results, the InGaN-based LED with the HLAPSS has a higher LOP than the one with the SLAPSS due to the weaker QCSE within multiple-quantum wells (MQWs).

8.
Opt Express ; 22 Suppl 5: A1222-8, 2014 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-25322176

RESUMO

InGaN/GaN-based solar cells with vertical-conduction feature on silicon substrates were fabricated by wafer bonding technique. The vertical solar cells with a metal reflector sandwiched between the GaN-based epitaxial layers and the Si substrate could increase the effective thickness of the absorption layer. Given that the thermally resistive sapphire substrates were replaced by the Si substrate with high thermal conductivity, the solar cells did not show degradation in power conversion efficiency (PCE) even when the solar concentrations were increased to 300 suns. The open circuit voltage increased from 1.90 V to 2.15 V and the fill factor increased from 0.55 to 0.58 when the concentrations were increased from 1 sun to 300 suns. With the 300-sun illumination, the PCE was enhanced by approximately 33% compared with the 1-sun illumination.

9.
Opt Express ; 21 Suppl 5: A864-71, 2013 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-24104581

RESUMO

GaN-based blue light-emitting diodes (LEDs) with micro truncated hexagonal pyramid (THP) array were grown on selective-area Si-implanted GaN (SIG) templates. The GaN epitaxial layer regrown on the SIG templates exhibited selective growth and subsequent lateral growth to form the THP array. The observed selective-area growth was attributed to the different crystal structures between the Si-implanted and implantation-free regions. Consequently, LEDs grown on the GaN THP array emitted broad electroluminescence spectra with multiple peaks. Spatially resolved cathodoluminescence revealed that the broad spectra originated from different areas within each THP. Transmission electron microscopy showed the GaN-based epitaxial layers, including InGaN/GaN multi-quantum wells regrown at different growth rates (or with different In content in the InGaN wells) between the semi-polar and c-face planes of each THP.

10.
Opt Express ; 21(24): 30065-73, 2013 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-24514556

RESUMO

This paper demonstrates that quantum-confined Stark effect (QCSE) within the multiple quantum wells (MQWs) can be suppressed by the growths of InGaN-based light-emitting diodes (LEDs) on the nano-sized patterned c-plane sapphire substrates (PCSSs) with reducing the space. The efficiency droop is also determined by QCSE. As verified by the experimentally measured data and the ray-tracing simulation results, the suppressed efficiency droop for the InGaN-based LED having the nano-sized PCSS with a smaller space of 200 nm can be acquired due to the weaker function of the QCSE within the MQWs as a result of the smaller polarization fields coming from the lower compressive strain in the corresponding epitaxial layers.

11.
Opt Express ; 20 Suppl 6: A1019-25, 2012 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-23187653

RESUMO

We present an efficient vertical InGaN light-emitting diode (LED) in which the proposed vertical LEDs were fabricated with patterned sapphire substrates (PSS) using thinning techniques. After the thinning of sapphire substrate, selective dry etching process was performed on the remainder sapphire layer to expose the n-GaN contact layer instead of removing the sapphire substrate using the laser lift-off technique. These processes feature the LEDs with a sapphire-face-up structure and vertical conduction property. The PSS was adopted as a growth substrate to mitigate the light-guided effect, and thereby increase the light-extraction efficiency. Compared with conventional lateral GaN LEDs grown on PSS, the proposed vertical LEDs exhibit a higher light output power and less power degradation at a high driving current. This could be attributed to the fact that the vertical LEDs behave in a manner similar to flip-chip GaN/sapphire LEDs with excellent heat conduction.

12.
Opt Express ; 20(1): A119-24, 2012 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-22379672

RESUMO

Vertical GaN-based light-emitting diodes (LEDs) were fabricated with a Si substrate using the wafer-bonding technique. Lapping and dry-etching processes were performed for thinning the sapphire substrate instead of removing this substrate using the laser lift-off technique and the thinning process associated with the wafer-bonding technique to feature LEDs with a sapphire-face-up structure and vertical conduction property. Compared with conventional lateral GaN/sapphire-based LEDs, GaN/Si-based vertical LEDs exhibit higher light output power and less power degradation at a high driving current, which could be attributed to the fact that vertical LEDs behave in a manner similar to flip-chip GaN/sapphire LEDs with excellent heat conduction. In addition, with an injection current of 350 mA, the output power (or forward voltage) of fabricated vertical LEDs can be enhanced (or reduced) by a magnitude of 60% (or 5%) compared with conventional GaN/sapphire-based LEDs.


Assuntos
Óxido de Alumínio/química , Gálio/química , Índio/química , Iluminação/instrumentação , Semicondutores , Desenho de Equipamento , Análise de Falha de Equipamento
13.
Opt Express ; 20(23): A1019-25, 2012 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-23326851

RESUMO

We present an efficient vertical InGaN light-emitting diode (LED) in which the proposed vertical LEDs were fabricated with patterned sapphire substrates (PSS) using thinning techniques. After the thinning of sapphire substrate, selective dry etching process was performed on the remainder sapphire layer to expose the n-GaN contact layer instead of removing the sapphire substrate using the laser lift-off technique. These processes feature the LEDs with a sapphire-face-up structure and vertical conduction property. The PSS was adopted as a growth substrate to mitigate the light-guided effect, and thereby increase the light-extraction efficiency. Compared with conventional lateral GaN LEDs grown on PSS, the proposed vertical LEDs exhibit a higher light output power and less power degradation at a high driving current. This could be attributed to the fact that the vertical LEDs behave in a manner similar to flip-chip GaN/sapphire LEDs with excellent heat conduction.

14.
Opt Express ; 19 Suppl 6: A1211-8, 2011 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-22109617

RESUMO

Up-converted heterostructures with a Mn-doped GaN intermediate band photodetection layer and an InGaN/GaN multiple quantum well (MQW) luminescence layer grown by metal-organic vapor-phase epitaxy are demonstrated. The up-converters exhibit a significant up-converted photoluminescence (UPL) signal. Power-dependent UPL and spectral responses indicate that the UPL emission is due to photo-carrier injection from the Mn-doped GaN layer into InGaN/GaN MQWs. Photons convert from 2.54 to 2.99 eV via a single-photon absorption process to exhibit a linear up-conversion photon energy of ~450 meV without applying bias voltage. Therefore, the up-conversion process could be interpreted within the uncomplicated energy level model.

15.
Opt Express ; 19(13): 12658-63, 2011 Jun 20.
Artigo em Inglês | MEDLINE | ID: mdl-21716508

RESUMO

In this study, gallium nitride (GaN)-based metal-insulator-semiconductor (MIS) ultraviolet (UV) photodetectors (PDs) with a gallium oxide (GaO(x)) gate layer formed by alternating current bias-assisted photoelectrochemical oxidation of n-GaN are presented. By introducing the GaO(x) gate layer to the GaN MIS UV PDs, the leakage current is reduced and a much larger UV-to-visible rejection ratio (R(UV/vis)) of spectral responsivity is achieved. In addition, a bias-dependent spectral response results in marked increase of the R(UV/vis) with bias voltage up to ~10(5). The bias-dependent responsivity suggests the possible existence of internal gain in of the GaN MIS PDs.


Assuntos
Gálio/química , Dispositivos Ópticos , Óptica e Fotônica/métodos , Semicondutores , Raios Ultravioleta , Eletrônica , Óptica e Fotônica/instrumentação , Processos Fotoquímicos
16.
Opt Express ; 19(13): 12719-26, 2011 Jun 20.
Artigo em Inglês | MEDLINE | ID: mdl-21716514

RESUMO

In this article, the characteristics of GaN-based LEDs grown on Ar-implanted GaN templates to form inverted Al0.27Ga0.83N pyramidal shells beneath an active layer were investigated. GaN-based epitaxial layers grown on the selective Ar-implanted regions had lower growth rates compared with those grown on the implantation-free regions. This resulted in selective growth, and formation of V-shaped concaves in the epitaxial layers. Accordingly, the inverted Al0.27Ga0.83N pyramidal shells were formed after the Al0.27Ga0.83N and GaN layers were subsequently grown on the V-shaped concaves. The experimental results indicate that the light-output power of LEDs with inverted AlGaN pyramidal shells was higher than those of conventional LEDs. With a 20 mA current injection, the output power was enhanced by 10% when the LEDs were embedded with inverted Al0.27Ga0.83N pyramidal shells. The enhancement in output power was primarily due to the light scattering at the Al0.27Ga0.83N/GaN interface, which leads to a higher escape probability for the photons, that is, light-extraction efficiency. Based on the ray tracing simulation, the output power of LEDs grown on Ar-implanted GaN templates can be enhanced by over 20% compared with the LEDs without the embedded AlGaN pyramidal shells, if the AlGaN layers were replaced by Al0.5Ga0.5N layers.


Assuntos
Compostos de Alumínio/química , Gálio/química , Dispositivos Ópticos , Pontos Quânticos , Óxido de Alumínio/química , Argônio/química , Fontes de Energia Elétrica , Eletrônica , Microscopia Eletrônica de Varredura
17.
Opt Express ; 19 Suppl 4: A695-700, 2011 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-21747536

RESUMO

InGaN/sapphire-based photovoltaic (PV) cells with blue-band GaN/InGaN multiple-quantum-well absorption layers grown on patterned sapphire substrates were characterized under high concentrations up to 150-sun AM1.5G testing conditions. When the concentration ratio increased from 1 to 150 suns, the open-circuit voltage of the PV cells increased from 2.28 to 2.50 V. The peak power conversion efficiency (PCE) occurred at the 100-sun conditions, where the PV cells maintained the fill factor as high as 0.70 and exhibited a PCE of 2.23%. The results showed great potential of InGaN alloys for future high concentration photovoltaic applications.

18.
Opt Express ; 18 Suppl 4: A562-7, 2010 Nov 08.
Artigo em Inglês | MEDLINE | ID: mdl-21165089

RESUMO

In this study, GaN-based light-emitting diodes (LEDs) with naturally formed oblique sidewall facets (OSFs) were fabricated through a selective regrowth process. The SiO2 mask layer was patterned on a heavily doped n-GaN template layer rather than on a sapphire substrate. As a result, the periphery of the LED included several OSFs around the regrown GaN mesa. While processing the device, dry etching was unnecessary for exposing the n-GaN underlying layer in order to form the n-type Ohmic contacts. This could be attributed to the fact that the n-GaN template layer with an electron concentration of around 8 × 10¹8/cm³ was exposed after the removal of the SiO2 mask layer. With an injection current of 20 mA, GaN-based LEDs with OSFs exhibited a 21% enhancement in light output compared with those that have vertical sidewall facets. The enhancement is attributed to the fact that photons extracted from OSFs can reduce internal absorption loss.

19.
J Environ Health ; 65(10): 9-14, 30, 2003 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-12800815

RESUMO

Media reporting of restaurant inspection results is a topic hotly debated by food service health inspectors. A survey of Indiana health inspectors was conducted to determine attitudes, preferences, and perceptions about the impact of media reporting. The survey showed that in the geographic areas of slightly fewer than half of the respondents, inspection results were already being reported in the media. The question of whether media reporting was advisable received mixed responses, with slightly over half favoring media reporting. Respondents were more likely to favor media reporting if they were from areas where inspection results were already being reported to the media, areas with larger populations, or areas in which more restaurant inspections were being done. Newspapers were the preferred venue for media reporting.


Assuntos
Contaminação de Alimentos , Inspeção de Alimentos , Meios de Comunicação de Massa , Opinião Pública , Revelação da Verdade , Atitude , Coleta de Dados , Humanos , Indiana , Restaurantes/normas , Saneamento
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