Characteristics of InGaN-based superluminescent diodes with one-sided oblique cavity facet

We have fabricated InGaN-based superluminescent diodes(SLDs)with one-sided oblique facet.The characteristics of the SLDs and laser diodes with the same cavity length(800 lm)were compared.The typical peak wavelength and the full width at half maximum of the spectrum in superluminescence regime are 445.3 and 7.7 nm for the SLDs with 800 lm cavity length.The characteristics of the SLDs with different cavity length were also demonstrated in a comparative way.It is found that the gain of the InGaN multi-quantum wells in blue spectral range is a linear function of the current density below gain saturation region.The lasing threshold current turns out to be higher for the shorter SLD(S-SLD)(400 lm),but the output light intensity of the longer SLD(800 lm)is higher than that of the S-SLD under the same current density.The gain saturation phenomenon was observed in S-SLD when it was biased at a current density larger than 27.5 kA/cm2.The increase of junction temperature was identified as the main reason for gain saturation through spectra analysis.

Light output improvement of GaN-based light-emitting diodes grown on Si (111) by a via-thin-film structure

This work reports the fabrication of via-thin-film light-emitting diode （via-TF-LED） to improve the light output power （LOP） of blue/white GaN-based LEDs grown on Si （111） substrates. The as-fabricated via-TF-LEDs were featured with a roughened n-GaN surface and the p-GaN surface bonded to a wafer carrier with a silver-based reflective electrode, together with an array of embedded n-type via pillar metal contact from the p-GaN surface etched through the multiple-quantum-wells （MQWs） into the n-GaN layer. When operated at 350 mA, the via-TF- LED gave an enhanced blue LOP by 7.8% and over 3.5 times as compared to the vertical thin-film LED （TF-LED） and the conventional lateral structure LED （LS-LED）. After covering with yellow phosphor that converts some blue photons into yellow light, the via-TF-LED emitted an enhanced white luminous flux by 13.5% and over 5 times, as compared with the white TF-LED and the white LS-LED, respectively. The significant LOP improve- ment of the via-TF-LED was attributed to the elimination of light absorption by the Si （111） epitaxial substrate and the finger-like n-electrodes on the roughened emitting surface.

Room-temperature continuous-wave electrically pumped InGaN/GaN quantum well blue laser diode directly grown on Si

Current laser-based display and lighting applications are invariably using blue laser diodes(LDs)grown on freestanding GaN substrates,which are costly and smaller in size compared with other substrate materials.1–3 Utilizing less expensive and large-diameter Si substrates for hetero-epitaxial growth of indium gallium nitride/gallium nitride(InGaN/GaN)multiple quantum well(MQW)structure can substantially reduce the cost of blue LDs and boost their applications.To obtain a high crystalline quality crack-free GaN thin film on Si for the subsequent growth of a blue laser structure,a hand-shaking structure was formed by inserting Al-composition step down-graded AlN/AlxGa1−xN buffer layers between GaN and Si substrate.Thermal degradation in InGaN/GaN blue MQWs was successfully suppressed with indium-rich clusters eliminated by introducing hydrogen during the growth of GaN quantum barriers(QBs)and lowering the growth temperature for the p-type AlGaN/GaN superlattice optical cladding layer.A continuous-wave(CW)electrically pumped InGaN/GaN quantum well(QW)blue(450 nm)LD grown on Si was successfully demonstrated at room temperature(RT)with a threshold current density of 7.8 kA/cm^(2).

Al-free cladding-layer blue laser diodes with a low aspect ratio in far-field beam pattern

c-plane GaN-based blue laser diodes（LDs） were fabricated with Al-free cladding layers（CLs） and deepened etching depth of mesa structure, so the aspect ratio of the far-field pattern（FFP） of the laser beam can be reduced to as low as 1.7, which is nearly the same as conventional AlGa In P-based red LDs. By using GaN CLs,the radiation angle of the laser beam θ⊥ is only 10.1° in the direction perpendicular to the junction plane. After forming a deeply etched mesa, the beam divergence angle parallel to the junction plane of FFP, θ;, increases from4.9° to 5.8°. After using the modified structure, the operation voltage of LD is effectively reduced by 2 V at an injection current of 50 mA, but the threshold current value increases. The etching damage may be one of the main reasons responsible for the increase of the threshold current.