Multiquantum-well Active Layer Research Articles

Comparative modeling results for ridge waveguide MQW and hybrid Si/III-V lasers

In this study, 1550 nm ridge waveguide multi quantum well (MQW) and hybrid Si/III-V lasers are simulated and the results are studied in a comparative setting. InGaAsP active layers with a ridge waveguide length of 500 μm and width of 5 μm with six quantum wells are chosen for both MQW and hybrid Si/III-V lasers. The hybrid Si/III-V laser structure is obtained by integration of a ridge waveguide MQW semiconductor laser with a silicon-on-insulator (SOI) chip. The proposed structure allows laser mode to experience maximal gain available in the III-V region while maintaining a high coupling efficiency to Si-waveguide. The results demonstrate that the optical power generated by MQW active layer can be transferred to the silicon waveguide of the hybrid Si/III-V laser. In addition, an increase in the threshold current and degeneration in the frequency response of the hybrid laser are observed compared to the MQW one. The results also indicate that there is not a big difference between the ridge waveguide MQW and the hybrid Si/III-V lasers in terms of spectrum and spontaneous emission characteristics.

Formation properties of an InGaN active layer for high-efficiency InGaN/GaN multi-quantum-well-nanowire light-emitting diodes

Nitride-based nanowires (NWs) have several advantages, such as flexibility in choosing a substrate, easy fabrication, large light-emitting area, no internal electric field, enhanced light extraction, and reduced defects by strain relief, that are useful for enhancing the efficiency of light-emitting diodes (LEDs). Here, we report how crucial the formation properties of the InGaN active layer are for enhancing the efficiency of core-shell InGaN/GaN multi-quantum-well (MQW)-NW LEDs that are selectively grown on oxide templates with perfectly-circular hole patterns. The nanostructures are analyzed for two types of LEDs, one containing defect-free MQW active layer and the other containing MQW layer with defects by using high-resolution transmission electron microscopy. The I-V curve of the defect-free LED shows a rectifying behavior with an on/off ratio of ~109, typical of a diode, and the off-state leakage current of the LED with defects is much larger than that of the defect-free LED, resulting in brighter electroluminescence from the latter device. These results suggest that well-defined nonpolar InGaN/GaN MQW-NWs can be utilized for the realization of high-performance LEDs.

Multichannel DFB Laser Arrays Fabricated by Upper SCH Layer SAG Technique

Multiwavelength laser arrays (MWLAs) fabricated by a novel upper separate confinement heterostructure (SCH) layer selective area growth (SAG) technique are studied in comparison with laser arrays fabricated by the conventional multiquantum well (MQW) SAG technique. For MWLAs by the MQW SAG, the range of the laser emission of the array is smaller than the span of the PL wavelengths of the MQW active layers. In addition, the material quality of the MQW layer degrades greatly as the width of the SAG strips is increased. Thus, the MWLAs fabricated by the method have scattered L-I characters and large fluctuation of wavelength spacings. In contrast, the MWLAs fabricated by the novel SAG method have much better wavelength spacing uniformity than those by MQW SAG, which is comparable to or better than the MWLAs fabricated by E-beam direct writing. Furthermore, the upper SCH layer SAG technique is suitable for the fabrication of MWLAs with wavelength interval, which is a challenge even for E-beam technique. In the SCH layer SAG, the MQW layer is untouched, and the same is true for all the laser elements in an array. The metal organic vapor phase epitaxies ability to control the material properties with high accuracy can be fully utilized for the fabrication of MWLAs. Combined with partially gain-coupled distributed feedback structures, the technique is promising for the fabrication of low-cost, high-quality MWLAs.

Amplifying characteristics of 1.55-/spl mu/m polarization-insensitive SOAs with MQW and strained-bulk active Layers for device application

Fundamental amplifying characteristics of 1.55-mum semiconductor optical amplifiers (SOAs) that contain multiquantum well (MQW) active layers with an optimized tensile strain or bulk active layers with various tensile strains were investigated. Both types of SOAs have their own merits and demerits. For device application in networks, driving current and wavelength in the low-polarization-sensitivity condition are very important, but they have not been clarified yet. The results of the present investigation clarify the driving current and wavelength characteristics of low-polarization-sensitivity SOAs with MQW and strained-bulk active layers. The low-polarization-sensitivity condition of SOAs with a strained-bulk active layer is shown to have a very wide range of driving current and wavelength for network-device application. These results, with other requirements taken into account, provide guidelines for choosing the type of SOA most suitable for a given application

High-efficiency InGaN-based light-emitting diodes with nanoporous GaN:Mg structure

In this research nanoporous structures on p-type GaN:Mg and n-type GaN:Si surfaces were fabricated through a photoelectrochemical (PEC) oxidation and an oxide-removing process. The photoluminescence (PL) intensities of GaN and InGaN∕GaN multi-quantum-well (MQW) structures were enhanced by forming this nanoporous structure to increase light extraction efficiency. The PL emission peaks of an MQW active layer have a blueshift phenomenon from 465.5nm (standard) to 456.0nm (nanoporous) measured at 300K which was caused by partially releasing the compressive strain from the top GaN:Mg layers. The internal quantum efficiency could be increased by a partial strain release that induces a lower piezoelectric field in the active layer. The thermal activation energy of a nanoporous structure (85meV) is higher than the standard one (33meV) from a temperature dependent PL measurement. The internal quantum efficiency and light extraction efficiency of an InGaN∕GaN MQW active layer are significantly enhanced by this nanoporous GaN:Mg surface, and this PEC treated nanoporous structure is suitable for high-power lighting applications.

Improved performance of 1.3 µm InGaAsP–InP lasers with an AlInAs electron stopper layer

We have fabricated 1.3 µm InGaAsP–InP strained-layer multi-quantum-well (MQW) lasers with an AlInAs electron stopper layer (ESL). The ESL was inserted between the MQW active layer and the p-side separate confinement heterostructure (SCH) layer to suppress electron leakage in the conduction band from the active region to the p-cladding layer. Lasers with an ESL exhibited much improved temperature characteristics of threshold current and external slope efficiency. As a result, a lower power penalty of 2.2 dB from 25 °C to 85 °C was achieved at an injected current of 60 mA. The insertion of an AlInAs ESL into the SCH layer is a successful way to realize the uncooled operation of 1.3 µm InGaAsP–InP lasers at high temperatures.

1.48-μm-wavelength ASM-DC-PBH LDs with extremely uniform lasing characteristics

High-power 1.48-/spl mu/m erbium-doped fiber amplifier pumping InGaAsP MQW laser diodes (LDs) have been investigated using all selective metal-organic vapor phase epitaxy grown (ASM) fabrication method. The method provided a precise dimension control of multiquantum-well active layers and current blocking layers, resulting in excellent current blocking characteristics and extremely uniform lasing characteristics even at high injection current. The average light output power of 262 mW at 1 A with a standard deviation of as small as 1.4 mW for 20 consecutive LDs has been achieved.

Pulse-mode Selective Metal-organic Vapor Phase Epitaxy Method for Migration Enhancement and High-quality Strained InGaAsP Multi-quantum Well Structure

A pulse-mode selective metal-organic vapor phase epitaxy (MOVPE) method for achieving excellent crystal quality of an InGaAsP strained multi-quantum well (MQW) structure on a narrow stripe region was investigated. The migration enhancement mechanism for pulse-mode epitaxy was studied from the view point of the decomposition state of group-III sources. By using the proposed method, the flatness of the selectively grown layers was drastically improved, and a very narrow photoluminescence spectrum linewidth of 28 meV at 25°C was realized for the strained MQW structure. The 1.3 µm-wavelength buried heterostructure (BH) laser diode (LD) with a strained MQW active layer grown by the pulse-mode selective MOVPE showed a very low-threshold current of 12 mA (18 mA) and high-slope efficiency of 0.37 (0.33) W/A at the high temperature of 85°C (100°C).

All-selective MOVPE-grown 1.3-μm strained multi-quantum-well buried-heterostructure laser diodes

Strained InGaAsP multi-quantum-well (MQW) double-channel planar-buried-hetero (DC-PBH) laser diodes (LDs) were fabricated by selective metalorganic-vapor-phase epitaxy (MOVPE). In the laser fabrication process, both the strained MQW active layer and current blocking structure were directly formed by selective MOVPE without any semiconductor etching process. The LDs are called all-selective MOVPE-grown BH LDs. The laser fabrication process can achieve both a precisely controlled gain waveguide structure and an excellent current blocking configuration, realizing the optimized DC-PBH structure. These aspects are essential to the high-performance and low-cost LD, which is strongly demanded for optical access network systems or fiber-to-the-home networks. This paper will show the excellent high-temperature characteristics for 1.3-/spl mu/m Fabry-Perot LDs which have a record threshold current of 18 mA with a low-operation current of 56 mA for 10 mW, and 74 mA for 15 mW at 100/spl deg/C with extremely high uniformity. Furthermore, reliable long-term operation at high temperature (85/spl deg/C) and high-output power of 15 mW has been demonstrated for the first time.

Low-damage dry-etched grating on an MQW active layer and dislocation-free InP regrowth for 1.55-/spl mu/m complex-coupled DFB lasers fabrication

A grating dry-etched through the upper wells of a multiquantum-well active layer has been characterized before and after regrowth. TEM observation and carrier lifetime measurements have shown growth-free defects of the epitaxial layers. As a consequence, quasi-100% monomode oscillation on /spl lambda/+1 mode has been achieved on complex-coupled distributed-feedback GaInAsP QW lasers fabricated with such grating.

InGaAs/AlGaInAs/InP Laser with Compressively Strained Multiquantum Well Layers for High Speed Modulation Bandwidth

The modulation frequency response of compressively strained multiquantum well (MQW) lasers grown with an InGaAs/AlGaInAs/InP heterostructure and emitting at the wavelength of 1.55 <FONT FACE="Symbol">m</font>m is presented. The laser devices processed with the mushroom-stripe buried structure present a high frequency 3 dB bandwidth above 20 GHz. The frequency response was measured with the small signal modulation technique. The logarithmic subtraction method was employed to extract the intrisic frequency response of the MQW active layer, providing the determination of important laser parameters: the differential gain, the nonlinear gain coefficient and the maximum 3 dB frequency bandwidth.

Low threshold and high uniformity for novel 1.3-/spl mu/m-strained InGaAsP MQW DC-PBH LDs fabricated by the all-selective MOVPE technique

1.3-μm-strained InGaAsP multiquantum-well (MQW) double-channel planar buried heterostructure laser diodes (DC-PBH-LDs) were fabricated by all-selective metalorganic vapor phase epitaxy (MOVPE). In the fabrication process, the strained MQW active layer and current-blocking structures were directly formed by selective MOVPE without a semiconductor etching process. A low-threshold current (I/sub th/=2.6 mA@25/spl deg/C for 200-μm-long 70%-90% facets) and excellent high-temperature operation (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =84 K, 25/spl deg/C-60/spl deg/C and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> =70 K, 25/spl deg/C-85/spl deg/C) were achieved. Furthermore, extremely uniform threshold current and slope efficiency were observed, The median time to failure for these LDs was estimated to be more than 100000 h under the 85/spl deg/C-5 mW aging condition.

Low-threshold strained multi-quantum well lasers fabricated by selective metalorganic vapor phase epitaxy without a semiconductor etching process

Strained InGaAsP multi-quantum well (MQW) buried hetero- (BH) laser diodes (LDs) on a p-InP substrate were fabricated by selective metalorganic vapor phase epitaxy (MOVPE). In the laser fabrication process, both the strained MQW active layer and current blocking structure were directly formed by selective MOVPE without a semiconductor etching process. This novel laser fabrication process produces extremely uniform device characteristics that are essential to the deployment of optical subscriber systems. Furthermore, important device design parameters (e.g. the active stripe shape or the leakage current path configuration) are precisely controlled by only the epitaxial growth steps. This highly controllable laser fabrication method results in a very low-threshold current with excellent uniformity (Ith = 1.78 ± 0.19 mA) for 20 consecutive LDs (L = 200 μm with 70%–90% coatings).

Temperature sensitivity of 1.54-μm vertical-cavity lasers with an InP-based Bragg reflector

We fabricated 1.54-/spl mu/m laser diodes that employ one integrated GaInAsP-InP and one Si-SiO/sub 2/ mirror in combination with a strain-compensated GaInAsP multiquantum-well active layer. Considerable care has to be taken of the temperature performance of the devices. Here, an important parameter is the gain offset between the gain peak wavelength and the cavity resonance. This offset is related to the experimentally accessible photoluminescence (PL) offset between the PL-peak wavelength and the emission wavelength. Vertical-cavity laser (VCL) characteristics such as threshold current and quantum efficiency show an extremely sensitive dependence on this parameter. In this paper, we focus on the temperature performance of our VCL's as a function of the cavity tuning. VCL's designed for PL-offset values between +17 and -16 mm are fabricated and characterized, As expected, the threshold current of all lasers shows a pronounced minimum at low temperatures. The position of this minimum depends on the offset at room temperature (RT) as a parameter. However, it turns out that the minimum threshold current is not obtained by matching gain peak and cavity wavelength for that temperature. The observed behavior is described well by calculations, taking into account the temperature dependence of the optical gain, of the cavity resonance, and of the cavity losses. The model is a valuable tool to tune the lasers for example low threshold current or reduced temperature sensitivity.

Room-temperature photo-pumped operation of 1.58-μm vertical-cavity lasers fabricated on Si substrates using wafer bonding

Long-wavelength vertical cavity lasers have been successfully fabricated on Si substrates using direct wafer bonding. InGaAs-InGaAsP multiquantum-well active layers with 40.5-pair InGaAsP-InP stacked mirrors have been directly bonded on 3.5-pair Al/sub 2/O/sub 3//a-Si mirrors deposited on Si substrates. The sample has been optically pumped at room temperature and lasing operation at 1.58-/spl mu/m has been achieved.

New Structure of 1.3 µm Strained-Layer Multi-Quantum Well Complex-Coupled Distributed Feedback Lasers

A new structure of 1.3 µm strained-layer multi-quantum well (MQW) complex-coupled distributed feedback lasers having an InAsP absorptive grating is demonstrated. In this structure, the InAsP absorptive grating and the strained-layer MQW active layer can be fabricated by a metalorganic vapor phase epitaxy process involving only one step. Furthermore, the fabricated laser has a low threshold current (16.8 mA) and a high efficiency (0.45 mW/mA).

Ultralow threshold 1.3-μm InGaAsP-InP compressive-strained multiquantum-well monolithic laser array for parallel high-density optical interconnects

An ultralow-threshold 1.3-/spl mu/m InGaAsP-InP 10-element monolithic laser array is achieved through careful optimization of a strained multiquantum-well active layer, especially the amount of strain, the well thickness, the barrier thickness, the number of wells, and the active laser width. This array has a record-low threshold current, highly uniform threshold current characteristics (1.3/spl plusmn/0.09 mA and slope efficiency of 0.37/spl plusmn/0.01 W/A), extremely low operating current of 14 mA under 5-mW output power, and long-term reliability. This array is suitable as light sources for a parallel high-density optical interconnection system. In addition, a record low CW threshold current of 0.58 mA at 20/spl deg/C and 1.62 mA at 90/spl deg/C, as a long-wavelength laser, is obtained by employing a short cavity (100 /spl mu/m) uith high-reflection coatings. >

Emission Properties of InGaAlP Visible Light-Emitting Diodes Employing a Multiquantum-Well Active Layer

Visible InGaAlP light-emitting diodes (LEDs) employing a multiquantum-well (MQW) active layer have been investigated. Photo luminescence measurements showed that growth on a GaAs substrate, with an intentional surface misorientation from the (100) plane towards the [011] direction, resulted in a marked improvement in the quality of the MQW compared with growth on a just (100) substrate. The emission properties of the LED strongly depended on the various parameters of the MQW structure, in particular the number of wells. The external quantum efficiency of a 600 nm LED with a 20-well MQW active layer was found to be 1.6%. The emission wavelength could be further reduced by 10 nm without any significant decrease in the external quantum efficiency.

Stable high-power operation of self-aligned stepped substrate (S3) AlGaInP visible laser diode with small beam aspect ratio

The authors have developed a selfaligned stepped substrate (S3) AlGaInP laser diode with a small beam aspect ratio and stable high-temperature high-output-power operation. The laser had the index-guided laser structure, and was fabricated by only one-step MOVPE. The width of the laser waveguide was decreased to enlarge the beam divergence in the horizontal direction. Also, the strained multiquantum-well active layer was modified to reduce the high temperature operation current by introducing GaInAsP well layers. As a result, the laser had a beam aspect ratio of 1.5 and stable 35 mW operation for more than 1000 h at 50°C.

Very low chirping of InGaAs-InGaAlAs MQW DFB BRS lasers under 10 Gbit/s modulation

The ability of the InGaAs/InGaAlAs multi-quantum-well (MQW) system to achieve ultra-low-chirp operation under 10-Gb/s operation is experimentally demonstrated. The MQW active layer has been grown by a solid-source molecular beam epitaxy (MBE) method. Two metalorganic chemical vapor deposition (MOCVD) regrowths were used to fabricate the distributed-feedback (DFB) buried ridge structure (BRS) lasers. DFB BRS lasers with good static and spectral performance have been obtained. Under 10-Gb/s modulation those lasers exhibited a chirp value as low as 0.11 nm at -20 dB, which is attributed to an extremely small phase-amplitude coupling coefficient of 1.8. An analysis of the AM and FM modulated laser field under digital pseudorandom signal confirms the observed spectra and shows the possibility of an optimum spectrum width for lasers with small chirping. >