A 10-GHz bandwidth electroabsorption modulated laser by ultra-low-pressure selective area growth

A novel integration technique has been developed using band-gap energy control of InGaAsP/InGaAsP multi-quantum-well (MQW) structures during simultaneous ultra-low-pressure (22 mbar) selective-area-growth (SAG) process in metal-organic chemical vapour deposition. A fundamental study of the controllability of band gap energy by the SAG method is performed. A large band-gap photoluminescence wavelength shift of 83nm is obtained with a small mask width variation (0-30 mu m). The method is then applied to fabricate an MQW distributed-feedback laser monolithically integrated with an electroabsorption modulator. The experimental results exhibit superior device characteristics with low threshold of 19 mA, over 24 dB extinction ratio when coupled into a single mode fibre. More than 10GHz modulation bandwidth is also achieved, which demonstrates that the ultra-low-pressure SAG technique is a promising approach for high-speed transmission photonic integrated circuits.

Monolithic integration of an InGaAsP-InP strained DFB laser and an electroabsorption modulator by ultra-low-pressure selective-area-growth MOCVD

The design and basic characteristics of a strained InGaAsP-InP multiple-quantum-well (MQW) DFB laser monolithically integrated with an electroabsorption modulator (EAM) by ultra-low-pressure (22 mbar) selective-area-growth (SAG) MOCVD are presented. A fundamental study of the controllability and the applicability of band-gap energy by using the SAG, method is performed. A large band-gap photoluminescence wavelength shift of 88 mn. was obtained with a small mask width variation (0-30 mu m). The technique is then applied to fabricate a high performance strained MQW EAM integrated with a DFB laser. The threshold current of 26 mA at CW operation of the device with DFB laser length of 300 mu m and EAM length of 150 mu m has been realized at a modulator bias of 0 V. The devices also exhibit 15 dB on/off ratio at an applied bias voltage of 5 V.

Photo-capacitance response of internal tunnelling coupling in quantum-dot-imbedded heterostructures under selective photo-excitation

Under selective photo-excitation, the capacitance response of internal tunnelling coupling in quantum-dots-imbedded heterostructures is studied to clarify the electronic states and the number densities of electrons filling in the quantum dots (QDs). The random nature for both optical transitions and the filling in a QD assembly makes highly resolved capacitance peaks appear in the C-V characteristic after turning off the photo-excitation.

Unveiling the morphology of buried In(Ga)As nanostructures by selective wet chemical etching: From quantum dots to quantum rings

The three-dimensional morphology of In(Ga)As nanostructures embedded in a GaAs matrix is investigated by combining atomic force microscopy and removal of the GaAs cap layer by selective wet etching. This method is used to investigate how the morphology of In(Ga)As quantum dots changes upon GaAs capping and subsequent in situ etching with AsBr3. A wave function calculation based on the experimentally determined morphologies suggests that quantum dots transform into quantum rings during in situ etching. (c) 2007 American Institute of Physics.

Fabrication of InGaAlAs MQW buried heterostructure lasers by narrow stripe selective MOVPE

Fabrication of InGaAlAs MQW buried heterostructure (BH) lasers by narrow stripe selective MOVPE is demonstrated in this paper. High quality InGaAlAs MQWs were first grown by narrow stripe selective MOVPE without any etching process and assessed by analysing the cross sections and PL spectrums of the InGaAlAs MQWs. Furthermore, BHs were fabricated for the InGaAlAs MQW lasers by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good device characteristics, with a high internal differential quantum efficiency of 85% and a low internal loss of 6.7 cm(-1). Meanwhile, narrow divergence angles of the far field pattern are obtained for the fabricated lasers.

Selective growth of absorptive InGaAsP layer on InP corrugation for a buried grating structure

A buried grating structure with a selectively grown absorptive InGaAsP layer was fabricated and characterized by scanning electron microscopy and photoluminescence. The InP corrugation was etched by introducing a SiO2 mask that was more stable than a conventional photoresist mask during the etching process. Moreover, the corrugation was efficaciously preserved during the selective growth of the absorptive layer with the SiO2 mask. Though this absorptive layer was only selectively grown on the concave region of the corrugation, it has a high intensity around the peak wavelength in comparison with that of InGaAlAs multiple quantum well, which was grown on the buried grating structure.

Narrow stripe selective growth of oxide-free InGaAlAs/InGaAlAs MQWs by ultra-low pressure MOVPE

Narrow stripe selective growth of oxide-free InGaAlAs/InGaAlAs multiple quantum wells (MQWs) has been successfully performed on patterned InP substrates by ultra-low pressure MOVPE. Flat and clear interfaces were obtained for the narrow stripe selectively grown MQWs under optimized growth conditions. These selectively grown MQWs were covered by specific InP layers, which can keep the MQWs from being oxidized during the fabrication of the devices. The characteristics of selectively grown MQWs were strongly dependent on the mask stripe width. In particular, a PL peak wavelength shift of 73 nm, a PL intensity of more than 57% and a PL FWHM of less than 102 meV were observed simultaneously with a small mask stripe width varying from 0 to 40 mu m. The results were explained by considering the migration effect from the masked region (MMR) and the lateral vapour diffusion effect (LVD).

AlGaInAs narrow stripe selective growth on substrates patterned with different mask designs

We have performed a narrow stripe selective growth of oxide-free A1GaInAs waveguides on InP substrates patterned with pairs of SiO2 mask stripes under optimized growth conditions. The mask stripe width varied from 0 to 40 mu m, while the window region width between a pair of mask stripes was fixed at 1.5, 2.5 or 3.5 mu m. Flat and smooth A1GaInAs waveguides covered by specific InP layers are successfully grown on substrates patterned with different mask designs. The thickness enhancement ratio and the photoluminescence (PL) spectrum of the A1GaInAs narrow stripe waveguides are strongly dependent on the mask stripe width and the window region width. In particular, a large PL wavelength shift of 79 nm and a PL FWHM of less than 64 meV are obtained simultaneously with a small mask stripe width varying from 0 to 40 mu m when the window region width is 1.5 mu m. We present some possible interpretations of the experimental observations in considering both the migration effect from a masked region and the lateral vapour diffusion effect.

Selective growth of InAs islands on patterned GaAs (100) substrate

By a combination of prepatterned substrate and self-organized growth, InAs islands are grown on the stripe-patterned GaAs (100) substrate by solid-source molecular beam epitaxy. It is found that the InAs quantum dots can be formed either on the ridge or on the sidewall of the stripes near the bottom, depending on the structure of the stripes on the patterned substrate or molecular beam epitaxy growth conditions. When a InxGa(1-x)As strained layer is grown first before InAs deposition, almost all the InAs quantum dots are deposited at the edges of the top ridge. And when the InAs deposition amount is larger, a quasi-quantum wire structure is found. The optical properties of the InAs dots on the patterned substrate are also investigated by photoluminescence. (c) 2005 Elsevier Ltd. All rights reserved.

Electroabsoorption-modulated laser light-source module using selective area growth for 10 Gb/s transmission

In this work, a novel light source of strained InGaAsP/InGaAsP MQW EAM monolithically integrated with DFB laser is fabricated by ultra-low-pressure (22 x 10(2) Pa) selective area growth ( SAG) MOCVD technique. Superior device performances have been obtained, sue h as low threshold current of 19 mA, output light power of about 7 mW, and over 16 dB extinction ratio at 5 V applied voltage when coupled into a single mode fiber. Over 10 GHz 3 dB bandwidth in EAM part is developed with a driving voltage of 3 V. After the chip is packaged into a 7-pin butterfly compact module, 10-Gb/s NRZ transmission experiments are successfully performed in standard fiber. A clearly-open eye diagram is achieved in the module output with over 8.3 dB dynamic extinction ratio. Power penalty less than 1.5 dB has been obtained after transmission through 53.3 km of standard fiber, which demonstrates that high-speed, low chirp EAM/DFB integrated light source can be obtained by ultra-low-pressure (22 x 102 Pa) SAG method.

10 GHz optical short pulse generation using tandem electroabsorption modulators monolithically integrated with distributed feedback laser by ultra-low-pressure selective area growth

In this work, a novel light source of tandem InGaAsP/InGaAsP multiple quantum well electroabsoption modulator( EAM ) monolithically integrated with distributed feedback laser is fabricated by ultra-low-pressure ( 22 x 10(2) Pa ) selective area growth metal-organic chemical vapor diposition technique. Superior device performances have been obtained, such as low threshold current of 19 mA, output light power of 4.5 mW, and over 20 dB extinction ratio at 5 V applied voltage when coupled into a single mode fiber. Over 10 GHz 3dB bandwidth in EAM part is developed with a driving voltage of 2 V. Using this sinusoidal voltage driven integrated device, 10 GHz repetition rate pulse with an actual width of 13.7 ps without any compression elements is obtained due to the gate operation effect of tandem EAMs.

Capacitance-voltage spectroscopy of In0.5Ga0.5As self-assembled quantum dots in double quantum wells under selective photo-excitation

Selectively photo-excited C-V spectroscopy has been measured in an In0.5Ga0.5As quantum dots (QDs)-embedded, three barrier-two well heterostructure. By comparing with a theoretical capacitance model, the pure capacitive contribution from In0.5Ga0.5As QDs, due to tunnelling coupling between In0.5Ga0.5As QDs and In0.18Ga0.82As quantum well, has been used to obtain the density of charges from photo-excited In0.5Ga0.5As QDs in a very straightforward manner.

Selective area growth of GaN on GaAs(001) substrates by metalorganic vapor-phase epitaxy

Selective area growth (SAG) of GaN on SiO2 stripe-patterned GaN/GaAs(001) substrates was carried out by metalorganic vapor-phase epitaxy. The SAG samples were investigated by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). SEM observations showed that the morphology of SAG GaN is strongly dependent on the window stripe orientation and slightly affected by the orientation relationship between the window stripes and the gas flow. The (I 1 1)B sidewalls formed on the SAG GaN stripes are found to be stable. XRD measurements indicated the full-widths at half-maximum (FWHMs) of cubic GaN (0 0 2) rocking curves are reduced after SAG. The measured FWHMs with omega-axis parallel to [1(1) over bar 0] are always larger than the FWHM values obtained with omega-axis parallel to [I 10], regardless of the orientation relationship between the w-axis and the GaN stripes. (C) 2003 Elsevier Science B.V. All rights reserved.

Selective-area MOCVD growth for distributed feedback lasers integrated with vertically tapered self-aligned waveguide

The growth pressure and mask width dependent thickness enhancement factors of selective-area MOCVD. grow th were investigated in this article. A, high enhancement of 5.8 was obtained at 130 mbar with the mask width of 70 mum. Mismatched InGaAsP (-0.5%) at the maskless region which could ensure the material at butt-joint region to be matched to InP was successively grown by controlling the composition and mismatch modulation in the selective-area growth. The upper optical confinement layer and the butt-coupled tapered thickness waveguide were regrown simultaneously in separated confined heterostructure 1.55 gm distributed feedback laser, which not only offered the separated optimization of the active region and the integrated spotsize converter, but also reduced the difficulty of the butt-joint selective regrowth. A narrow beam of 9degrees and 12degrees in the vertical and horizontal directions, a low threshold current of 6.5 mA was fabricated by using this technique. (C) 2003 Elsevier Science B.V. All rights reserved.

Investigation on the origin of crystallographic tilt in lateral epitaxial overgrown GaN using selective etching

The crystallographic tilt of the lateral epitaxial overgrown (LEO) GaN on sapphire Substrate with SiNx mask is investiaated by double crystal X-ray diffraction. Two wing peaks beside the GaN 0002 peak can be observed for the as-grown LEO GaN. During the selective etching of SiNx mask, each wing peak splits into two peaks, one of which disappears as the mask is removed, while the other remains unchanged. This indicates that the crystallographic tilt of the overgrown region is caused not only by the plastic deformation resulted from the bending of threading dislocations, but by the non-uniformity elastic deformation related with the GaN, SiNx interfacial forces. The widths of these two peaks are also studied in this paper. (C) 2002 Elsevier Science B.V. All rights reserved.