Quantum-well Active Region Research Articles

Performance of an optical amplifier/modulator based on a diode laser

The performed numerical simulation shows that the main parameter determining the performance of an optical amplifier/modulator is the stimulated-emission cross section (differential gain) in the active region. A cross section of ∼3×10-15 cm2, which is quite realistic for modern heterostructures with quantum-well active regions, may provide an amplifier/modulator performance sufficient for data transfer at a rate of ∼20 Gbit s-1.

Boosting Green GaInN/GaN Light-Emitting Diode Performance by a GaInN Underlying Layer

The light output of 530 nm green GalnN/GaN light-emitting diodes on sapphire has been nearly doubled by the insertion of a 130-nm GalnN underlayer (UL) between the n-GaN electron injection layer and the quantum-well (QW) active region. Under variation of the alloy composition, best results were obtained for an x = 6.3% Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> N UL. By low-temperature depth-resolved cathodoluminescence spectroscopy, an interplay of the impurity-related donor-acceptor pair recombination, the UL, and the QW emission has been observed. We propose that the resonance and level alignments between the defect and UL levels reroute excitation toward radiative recombination in the QWs.

Optical gain characteristics of staggered InGaN quantum wells lasers

Staggered InGaN quantum wells (QWs) are analyzed as improved gain media for laser diodes (LDs) lasing at 440 and 500 nm. The calculation of band structure is based on a 6-band k⋅p method taking into account the valence band mixing, strain effect, and spontaneous and piezoelectric polarizations as well as the carrier screening effect. Staggered InGaN QWs with two-layer and three-layer step-function like In-content InGaN QWs structures are investigated to enhance the optical gain as well as to reduce the threshold current density for LDs emitting at 440 and 500 nm. Our analysis shows that the optical gain is enhanced by 1.5–2.1 times by utilizing the staggered InGaN QW active region emitting at 440 nm, which leads to a reduction of the threshold current density up to 24% as compared to that of the conventional InGaN QW laser. Staggered InGaN QWs with enhanced optical gain shows significantly reduced blue-shift as carrier density increases, which enables nitride QWs with high optical gain in the green spectral regime. The use of green-emitting three-layer staggered InGaN QW is also expected to lead to reduction in the threshold carrier density by 30%.

Electroluminescence induced by photoluminescence excitation in GaInN/GaN light-emitting diodes

Optical emission resulting from 405 nm selective photoexcitation of carriers in the GaInN/GaN quantum well (QW) active region of a light-emitting diode reveals two recombination channels. The first recombination channel is the recombination of photoexcited carriers in the GaInN QWs. The second recombination channel is formed by carriers that leak out of the GaInN QW active region, self-bias the device in forward direction, induce a forward current, and subsequently recombine in the GaInN active region in a spatially distributed manner. The results indicate dynamic carrier transport involving active, confinement, and contact regions of the device.

Continuous wave operated 3.2 µm type-I quantum-well diode lasers with the quinary waveguide layer

GaSb-based diode lasers with type-I quantum-well active region located either in the center of quinary AlInGaAsSb broadened waveguide or shifted to the p-cladding side were fabricated and characterized. Devices with narrower ‘p-side waveguide’ demonstrate better performance. We explain the phenomenon by reduced hole concentration in the waveguide region of the device. At 12 °C, lasers with optimized design generate above 65 mW of continuous wave output power at 3.2 µm.

Effect of Residual Stress and Sidewall Emission of InGaN-Based LED by Varying Sapphire Substrate Thickness

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> The effect of residual stress and the sidewall emission in InGaN–GaN films with different thickness of sapphire substrate were investigated. The peak wavelength of electroluminescence was blue-shifted as thinning the sapphire substrate, because the wafer bowing-induced mechanical stress alters the piezoelectric field in the InGaN–GaN multiple quantum-well active region of the light-emitting diode (LED). A sideview LED with 170-<formula formulatype="inline"><tex Notation="TeX">$\mu\hbox{m}$</tex> </formula>-thick sapphire exhibited the highest output power of 14.04 mW at a forward current of 20 mA, improved by 7% compared to that with 80-<formula formulatype="inline"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula>-thick sapphire. The maximum output power can be obtained by considering both the photon escaping probability from the edges of the sapphire and the photon absorption probability in the sapphire as well as the residual mechanical stress induced by the wafer bowing. </para>

Control of Quantum-Confined Stark Effect in InGaN-Based Quantum Wells

This paper reviews current technological developments in polarization engineering and the control of the quantum-confined Stark effect (QCSE) for InxGa1- xN-based quantum-well active regions, which are generally employed in visible LEDs for solid-state lighting applications. First, the origin of the QCSE in III-N wurtzite semiconductors is introduced, and polarization-induced internal fields are discussed in order to provide contextual background. Next, the optical and electrical properties of InxGa1- xN-based quantum wells that are affected by the QCSE are described. Finally, several methods for controlling the QCSE of InxGa1- xN-based quantum wells are discussed in the context of performance metrics of visible light emitters, considering both pros and cons. These strategies include doping control, strain/polarization field/electronic band structure control, growth direction control, and crystalline structure control.

Tilted-charge high speed (7 GHz) light emitting diode

We demonstrate a higher speed form of light emitting diode (LED), an asymmetrical two-junction tilted-charge LED, utilizing an n-type buried “drain” layer beneath the p-type “base” quantum-well (carrier and photon) active region. The drain layer tilts and pins the charge in the manner of a heterojunction bipolar light emitting transistor (HBLET), selecting and allowing only “fast” recombination (recombination lifetime τB of the order of base transit time τt). The tilted-charge LED, simple in design and construction, is capable of operation at low current in spontaneous recombination at a 7 GHz bandwidth or even higher with more refinement.

Effect of Silicon Doping in the Quantum-Well Barriers on the Electrical and Optical Properties of Visible Green Light-Emitting Diodes

The effect of Si doping in the GaN quantum-well (QW) barriers of the InGaN-GaN multiple QW active region in visible green light-emitting diodes (LEDs) was studied. As the doping level of Si increases, the intensity of electroluminescence (EL) decreases, while the forward voltage of the diodes is improved. Degradation of EL is believed to be mainly due to the hole transport blocking effect caused by Si doping in the QW barriers resulting in increased potential barriers. This effect is believed to be more significant in green LEDs than in violet and blue LEDs.

Plasmonic light-emission enhancement with isolated metal nanoparticles and their coupled arrays

We present a systematic study of the enhancement of radiative efficiency of light-emitting matter achieved by proximity to metal nanoparticles. Our goal is to ascertain the limits of the attainable enhancement. Two separate arrangements of metal nanoparticles are studied, namely isolated particles and an array of particles. The method of analysis is based on the effective mode volume theory. Using the example of an InGaN∕GaN quantum-well active region positioned in close proximity to Ag nanospheres, we obtain optimal parameters for the nanoparticles for maximum attainable enhancement. Our results show that while the enhancement due to isolated metal nanoparticles is significant, only modest enhancement can be achieved with an ordered array. We further conclude that a random assembly of isolated particles holds an advantage over the ordered arrays for light-emitting devices of finite area.

Self-consistent gain analysis of type-II ‘W’ InGaN–GaNAs quantum well lasers

Type-II InGaN–GaNAs quantum wells (QWs) with thin dilute-As (∼3%) GaNAs layer are analyzed self-consistently as improved III-nitride gain media for diode lasers. The band structure is calculated by using a six-band k⋅p formalism, taking into account valence band mixing, strain effect, spontaneous and piezoelectric polarizations, as well as the carrier screening effect. The type-II InGaN–GaNAs QW structure allows large electron-hole wave function overlap by confining the hole wave function in the GaNAs layer of the QW. The findings based on self-consistent analysis indicate that type-II InGaN-GaNAs QW active region results in superior performance for laser diodes, in comparison to that of conventional InGaN QW. Both the spontaneous emission radiative recombination rate and optical gain of type-II InGaN–GaNAs QW structure are significantly enhanced. Reduction in the threshold current density of InGaN–GaNAs QW lasers is also predicted.

Electroluminescence efficiency enhancement using metal nanoparticles

We apply the “effective mode volume” theory to evaluate enhancement of the electroluminescence efficiency of semiconductor emitters placed in the vicinity of isolated metal nanoparticles and their arrays. Using the example of an InGaN∕GaN quantum-well active region positioned in close proximity to Ag nanospheres, we show that while the enhancement due to isolated metal nanoparticles is large, only modest enhancement can be obtained with ordered array of those particles. We further conclude that random assembly of isolated particles holds an advantage over the ordered arrays for light emitting devices of finite area.

Combined analytical-finite difference time-domain full wave simulation of mode-locked vertical-extended-cavity semiconductor lasers

A time-domain approach based on the finite difference time-domain (FDTD) method is described for vertical-extended-cavity surface-emitting lasers (VECSELs). To permit the simulation of realistic devices with large extended cavities a combined analytical-FDTD model is developed. This approach uses plane wave propagation in the linear extended cavity to couple the active mirror and the semiconductor saturable absorber mirror (SESAM) in which the standard FDTD method is applied. This allows for a significant computational time reduction. The material response in the active quantum wells (QWs) and the absorber is incorporated by an infinite impulse response digital filter. The model is validated by the simulation of a passively mode-locked VECSEL with a multiple QW active region and a single QW SESAM.

Blue InGaN/GaN Light-Emitting Diodes Using Mg-Doped AlGaN Electron-Blocking Barriers

Blue InGaN/GaN multiple-quantum-well light-emitting diodes were grown on sapphire substrates by using a metal-organic vapor phase epitaxy system. A Mg-doped AlGaN electron-blocking barrier was introduced under various Cp2Mg ow conditions at a high temperature of 1050 C. The characterization included current-voltage, capacitance-voltage and electroluminescence analyses. The luminescence e ciency showed an improvement of more than 90 % when the Cp2Mg ow rate was increased from 50 to 200 sccm. The forward voltage was reduced to 3.18 V at 20 mA. The series resistance was also estimated to be 10.81 . Secondary-ion mass spectrometry revealed the Mg doping pro les close to the quantum-well active region. The increased Mg concentration resulted in improved hole injection and carrier concentration. This is in agreement with the increased electroluminescence e ciency and luminous intensity and with the lower turn-on voltage. The Xray di raction study showed a full width at half maximum of 290.1 arcsec from the GaN (0002) di raction and 325.9 arcsec from the GaN (10 12) di raction.

Room temperature operated 3.1μm type-I GaSb-based diode lasers with 80mW continuous-wave output power

High-power diode lasers with heavily strained In(Al)GaAsSb type-I quantum-well active regions emitting at 3.1μm at room temperature are reported. The devices produce continuous-wave output powers above 200mW at 250K and 80mW at 285K.

Influence of the InGaAs/(Al)GaAs quantum-well heterostructure growth features on the spectral characteristics of laser diodes

An abrupt decrease in the lasing wavelength was observed with increasing the pump current in injection semiconductor lasers emitting in the spectral range from 1050 to 1080 nm. The consideration of segregation phenomena, which strongly distort the nominal profile of the quantum-well active region of InGaAs/(Al)GaAs laser heterostructures during their growth, made it possible to calculate the energy spectrum of these heterostructures, which agrees with the results of spectral measurements. The energy levels of dimensional quantisation involved in lasing with decreasing the laser wavelength are identified based on the calculation.

The impact of hot-phonons on the performance of 1.3µm dilute nitride edge-emitting quantum well lasers

A robust opto-electronic device simulation tool is extended to model the phonon bottleneck in edge-emitting 1.3µm InGaAsN double quantum well (QW) laser diodes. Both the steady state operation and the transient response of the phonon bottleneck are examined as a function of injection current and heatsink temperature. It is found that the hot phonon population can raise the electron and hole temperatures in the QW active region by up to 7K above the equilibrium lattice temperature at moderate injection currents. At high injection currents, it is found that the phonon bottleneck can significantly decrease the optical power.

Threshold analysis of highly detuned long-wavelength GaAs-based GaInNAsSb/GaNAsQWVCSELs

Comprehensive 3D optical–electrical–thermal-gain self-consistent simulation of physical processes taking place inside a laser volume of the GaAs-based GaInNAsSb/GaNAs quantum-well (QW) vertical-cavity surface-emitting diode laser (VCSEL) is carried out to examine a possibility to reach the long-wavelength room-temperature (RT) continuous-wave (CW) laser operation in highly detuned devices. The RT CW 1.422-μm lasing emission has been found to be reached practically without troubles. However, to reach the 1.5-μm laser wavelength, it is necessary to increase the QW active region temperature by about 100K, which may be done by a proper increase in the RT CW operation current.

Self-consistent model of 650 nm GaInP/AlGaInP quantum-well vertical-cavity surface-emitting diode lasers

A comprehensive fully self-consistent model of oxide-confined GaAs-based vertical-cavity surface-emitting diode lasers (VCSELs) with GaInP/AlGaInP quantum-well active regions to simulate their room-temperature (RT) continuous-wave (CW) operation is presented. The model takes into consideration all observed or expected special features of GaInP/AlGaInP VCSELs. A complete set of model parameters is given. The model enables a deeper understanding of a VCSEL operation with full complexity of many inter-related physical phenomena taking place within its volume. It may also be used to design and optimize the above VCSEL structures for their numerous applications, in particular as sources of the 650 nm carrier wave in communication systems using plastic optical fibres. With the aid of this model, anticipated VCSEL RT CW performance characteristics may be determined.

High-Confinement Strained MQW for Highly Polarized High-Power Broadband Light Source

This letter presents highly polarized edge light-emitting diodes with high-confinement, strained, multiple quantum-well active regions. We demonstrate +40 dB of polarization extinction along with 16 dBm of output power from an 800-mum-long centered quantum-well device. By characterizing the polarization extinction and gain of devices with different lengths and optical confinement, we show that the polarization extinction is dominated by the polarization sensitivity of the gain