P-type Distributed Bragg Reflector Research Articles

A Comparative Study of Electrical Characterization of P-Doped Distributed Bragg Reflectors Mirrors for 1300 nm Vertical Cavity Semiconductor Optical Amplifiers

This paper presents an electrical analysis of various diameters of two p-types of GaAs/Al0.9Ga0.1As and two p-types of GaAs/Al0.3Ga0.7As/Al0.9Ga0.1As distributed Bragg reflectors (DBRs) mirrors structure grown on undoped and on p-doped GaAs, which affects the characteristics of 1300 nm vertical cavity surface emitting lasers (VCSELs) and vertical cavity semiconductor optical amplifiers (VCSOAs). Electrical characterizations and Hall measurements of current−voltage (IV) for GaAs/Al0.9Ga0.1As linear DBRs and GaAs/Al0.3Ga0.7As/Al0.9Ga0.1 As graded DBRs were also performed at temperatures between 13 and 300 K. Consequently, p-type DBRs are designed with graded composition interfaces technique. The smaller mesa diameters are used to reduce vertical and longitudinal resistances and to limit the heating effect and improve the characteristics of VCSEL/VCSOA devices.

Optical Characterizations of VCSEL for Emission at 850 nm with Al Oxide Confinement Layers

In-plane micro-photoluminescence (μ-PL) and micro-reflectivity measurements have been performed at room temperature by optical excitation perpendicular to the surface of two different structures: a complete vertical surface-emitting laser (VCSEL) structure and a VCSEL without the upper p-type distributed Bragg reflector (P-DBR). The two structures were both laterally oxidized and measurements were made on the top of oxidized and unoxidized regions. We show that, since the photoluminescence (PL) spectra consist of the cumulative effect of InGaAs/AlGaAs multi-quantum wells (MQWs) luminescence and interferences in the DBR, the presence or not of the P-DBR and oxide layers can significantly modify the spectrum. μ-PL mapping performed on full VCSEL structures clearly shows oxidized and unoxidized regions that are not resolved with visible light optical microscopy. Finally, preliminary measurements of the degree of polarization (DOP) of the PL have been made on a complete VCSEL structure before and after an oxidation process. We obtain an image of DOP measured by polarization-resolved μ-PL. These measurements allow us to evaluate the main components of strain.

Number of p-type distributed Bragg reflectors effects on gallium nitride (GaN)-based vertical cavity surface emitting laser performance

This paper has presented the characteristic features of the reflectivity of the output mirror at 415 nm vertical cavity surface emitting lasers with various distributed Bragg reflectors pairs. For this, vertical cavity surface emitting lasers with various corresponding p-distributed Bragg reflectors pairs are simulated using integrated system engineering simulation program. The output power and the threshold current for each of these devices were determined. We found that by increasing distributed Bragg reflectors pairs, the distributed Bragg reflectors reflectivity increased, which can reduce the device lasing threshold. However, the external differential quantum efficiency was inversely related to top mirror reflectivity. So, the optical output of the device also decreased with increased p-type mirror pairs. A suitable distributed Bragg reflectors design is carefully selected for the pair number so as to balance among low lasing threshold current, high output power, and high efficiency. Key words: Semiconductor lasers, vertical cavity surface emitting laser, distributed Bragg reflectors, external quantum efficiency, multiple quantum well.

Threshold control in VCSELs by proton implanted depth

The proton implantation is one of key procedures to confine the current diffusion in vertical cavity surface emitting lasers (VCSELs), in which the proton implanted depth and profile are main parameters. Threshold characteristics of VCSELs with various proton implanted depths are studied after optical, electrical and thermal fields have been simulated self-consistently in three dimensions. It is found that for VCSELs with confinement radius of 2 μm, increasing proton implanted depth can reduce the injected current threshold power and enhance the laser temperature in active region. Numerical results also indicate that there are optimal values for current aperture in proton implanted VCSELs. The minimum injected current threshold can be achieved in VCSELs with proton implantation near the active region and confinement radius of 1.5 μm, while the VCSELs with proton implantation in the middle of p-type distributed Bragg reflectors (DBRs) and confinement radius of 2.5 μm can realize the minimum temperature.

High-power vertical-cavity surface-emitting laser with an optimized p-contact diameter

A 980 nm bottom-emitting vertical-cavity surface-emitting laser (VCSEL) with a p-contact diameter is reported to achieve high power and good beam quality. A numerical simulation is conducted on the current spreading in a VCSEL with oxidation between the active region and the p-type distributed Bragg reflector. It is found that, for a particular oxide aperture diameter, somewhat homogeneous current distribution can be achieved for a VCSEL with an optimized p-contact diameter. The far-field divergence angle from a 600 microm diameter VCSEL is suppressed from 30 degrees to 15 degrees, and no strong sidelobe is observed in the far-field pattern by using the optimized p-contact diameter. There is a slight rise in threshold and optical output power that is due to the p-contact optimization. By improving the device packaging method, the maximum optical output power of the device is 2.01 W.

高功率径向桥电极垂直腔面发射激光器的研制

We report the fabrication of a novel high-power vertical-cavity surface-emitting laser (VCSEL) with radial bridge electrodes in this letter. The analysis shows that the radial bridge electrodes can reduce the p-type distributed Bragg reflector (p-DBR) electric and thermal resistance, and improve the device beam quality. The high-power radial brigde electrode VCSELs with 200-\mum aperture have been made and tested. The testing results show that the differential resistance of the VCSEL is 0.43 \Omega and the maximal continuous-wave (CW) output power is 340 mW, 1.7 times higher than the conventional electrode device. Its thermal resistance is 0.095 \Degress/mW, and its near-field pattern exhibits a homogeneous distribution. The high-power radial bridge electrode VCSEL has better temperature and opto-electric characteristics.

Polarization Switching in Vertical-Cavity Surface-Emitting Lasers by Asymmetrical Current Injection

Polarization switching between two orthogonal linear polarizations was experimentally demonstrated in newly designed 980-nm vertical-cavity surface-emitting lasers ( VCSELs ). A square-shaped mesa structure was prepared in a p-type distributed Bragg reflector mirror. Four p-side electrodes were placed in contact with the four sides of the square mesa. When the same current was injected into the four electrodes, the VCSEL oscillated with 0 or 90 linear polarizations. When the current was asymmetrically injected (the same current for two electrodes on the opposite sides of the square, but different for neighboring electrodes), the direction of the linear polarization became perpendicular to the direction of the line connecting the two electrodes injected with the larger current. It was confirmed that the VCSELs oscillated with a single frequency and the lowest order transverse mode in all cases.

Polarization Control of Vertical-Cavity Surface-Emitting Lasers by Utilizing Surface Plasmon Resonance

We demonstrate polarization control of vertical-cavity surface-emitting lasers (VCSELs) to any desired directions by utilizing surface plasmon resonance at a metal nanohole array. A silver nanohole array is integrated on the p-type distributed Bragg reflector of an 850-nm AlGaAs-GaAs-based VCSEL. The metal nanohole array placed at rectangular lattices with orthogonally different two periods, one of which meets the resonaint condition, exhibits strong polarization preference in optical transmission. Integrated four VCSELs with different directions of the rectangular arrays of nanoholes demonstrate successful control of the polarization angles. The VCSELs are closely located onto a one chip so that the optical outputs are easily coupled to one optical fiber. The presented VCSEL array will open a new horizon of multi-input multi-output communication systems by using polarization multiplexing.

Modal behavior of photonic-crystal vertical-cavity surface-emitting diode laser analyzed with Plane Wave Admittance Method

A three-dimensional, full vectorial model has been applied for investigation the modal characteristics of a phosphide photonic-crystal vertical-cavity surface-emitting diode laser. The photonic crystal has been defined as a regular, hexagonal net of holes, etched in the upper, p-type Distributed Bragg Reflector of the laser. The electromagnetic field has been confined to the active region by a single defect of the photonic crystal providing overlapping with carriers funneled by a tunnel junction. We have determined the range of design parameters, which provide single mode operation.

Effect of Annealing on Low-Threshold-Current Large-Wavelength InGaAs Quantum Well Vertical-Cavity Laser

An emission wavelength record emission wavelength of 1245 nm in double InGaAs/GaAs quantum wells without a strain-compensated barrier is obtained by metalorganic chemical vapor deposition (MOCVD). The effect of annealing on highly strained InGaAs quantum wells is analyzed using phtoluminanescence spectra. By comparing devices p-type distributed Bragg reflector (p-DBR) growth temperatures, the preliminary results indicate that a device with a low p-DBR growth temperature of 670°C exhibits a low threshold current and a high light output power. A threshold current of 6.7 mA in an InGaAs vertical-cavity surface emitting laser (VCSEL) in CW operation is realized with an emission spectrum up to 1.26 µm.

Implant isolation of AlGaAs multilayer DBR

AlGaAs distributed Bragg reflector (DBR) structures isolation by proton irradiation was studied. The evolution of n- and p-type DBR structures lateral sheet resistance with the irradiated proton dose was measured. The vertical isolation behavior was also obtained and compared to the lateral one. No significant differences were observed. The implantation maximum energy for these structures was estimated. Thermal stability of DBR vertical isolation was studied. A 500 °C stability was obtained for samples implanted to a dose 2.5 times greater than the threshold dose of isolation.

High Reflectivity p-Type Doped Distributed Bragg Reflectors Using ZnSe/MgS Superlattices

Undoped and p-type doped distributed Bragg reflectors (DBRs) have been grown by molecular beam epitaxy using ZnSe layers for the high refractive index material and ZnSe/MgS superlattices (SLs) for the low index material. The ZnSe/MgS SLs consist of 22.5 periods with a period length of 2.5 nm as confirmed by high-resolution X-ray diffraction measurements. A reflectivity of the p-type doped DBR higher than 99% at 522 nm has been achieved. The low temperature photoluminescence spectrum of the p-type doped DBR shows a strong donor-acceptor pair recombination peak at 2.686 eV.

Investigation of Green Emitting Monolithic II-VI Vertical Cavity Surface Emitting Laser

AbstractIn this paper, we are investigating the growth of a ZnSe based vertical cavity surface emitting laser (VCSEL). Undoped and p-type doped distributed Bragg reflectors (DBRs) with reflectivities exceeding 99% have been grown by molecular beam epitaxy (MBE) using Zn(S)Se layers for the high refractive index material and ZnSe/MgS superlattices (SLs) for the low index material. An undoped monolithic VCSEL structure containing a ZnCdSSe quantum well (QW) emitting in the blue-green reaches a quality factor (Q-factor) of 100, which is the best value reported so far. Temperature dependent photoluminescence (PL) measurements show that the emission of the QW is effectively guided by the cavity resonance.

GaInNAs/GaAs Multiple-Quantum WellResonant-Cavity-Enhanced Photodetectors at 1.3 µm

A GaInNAs/GaAs multiple quantum well (MQW) resonant-cavity enhancedphotodetector (RCE-PD) operated at a wavelength of 1.3 µm with thefull width at half maximum of 4 nm has been demonstrated.The GaInNAs RCE-PD was grown bymolecular beam epitaxy using a homemade ion-removed dc plasma cell asa nitrogen source. GaInNAs/GaAs MQW shows a strong exciton peak at roomtemperature, which is very beneficial for applications in long-wavelengthabsorption devices. For a 100 µm diameter RCE-PD, the dark current is20 and 32 pA at biases of 0 and 6 V, respectively, and the breakdown voltageis -18 V. The measured 3 dB bandwidth is 308 MHz, which is limited by theresistance of p-type distributed Bragg reflector mirror. The tunablewavelength in a range of 18 nm with the angle of incident light was observed.

Polarization selection in VCSELs due to current carrier heating

The problem of polarization switching of light from a vertical cavity surface emitting laser (VCSEL) is discussed. It is shown that heating of holes in the p-type distributed Bragg reflector and of electrons and holes in the quantum wells of the active region lead to switching of the polarization of the VCSEL. The model developed here makes it possible to explain the results of experiments on switching of the polarization of VCSELs at fixed active region temperatures.

Low-resistance visible wavelength distributed Bragg reflectors using small energy band offset heterojunctions

Semiconductor alloy heterojunctions, with compositions selected to achieve small band offset energies, were used in distributed Bragg reflector (DBR) structures for the purpose of lowering the vertical series resistance. The heterojunctions were simple abrupt interfaces without composition grading. 40 period mirrors of AlGaInP/Al(Ga)As layer pairs were grown by gas-source molecular beam epitaxy. Mirror reflectance values were found to be greater than 99% at wavelengths near 650 nm. Measured specific resistance values, 2.8×10−4 Ω cm2 for a p-type DBR and 2.6×10−5 Ω cm2 for a n-type DBR, were comparable to or better than (Al)GaAs/Al(Ga)As DBRs employing various graded interface composition designs.

Low threshold current vertical-cavity surface-emitting lasers grown at a fixed temperature

We report a successive growth of low threshold current GaAs/InGaAs/AlGaAs vertical cavity surface-emitting lasers by molecular beam epitaxy at a constant substrate temperature which is compromised for both InGaAs and AlGaAs materials. The layer thickness in the whole device structure, including the active region consisting of three quantum wells, n-type and p-type distributed bragg reflectors, can be monitored and controlled by using a system including an infrared pyrometer during growth. It is demonstrated that the multiple quantum well laser devices grown under such conditions show an threshold current as low as 700 μA from an etched squire of 15×15 μm2, about 310 Acm−2, at room temperature continuous wave operation, and a maximum output power of 800 μW at a lasing wavelength of 945 nm.

A low-threshold polarization-controlled vertical-cavity surface-emitting laser grown on GaAs (311)B substrate

We have demonstrated a GaAs (311)B vertical-cavity surface-emitting laser (VCSEL) with a threshold current as low as 250 /spl mu/A, which is the lowest value ever reported for that on non-(100) oriented substrates. Also, the fabricated VCSEL shows a stable polarization state for wide during current ranges and a large polarization-mode suppression ratio over 30 dB between the [233] and [011] axis modes at 5 mA. The electrical specific resistance of 1.2/spl times/10/sup -4/ /spl Omega//spl middot/cm/sup -2/ at the threshold was reasonably low due to carbon autodoping to AlAs in a p-type distributed Bragg reflector (DBR).

Growth of vertical-cavity surface-emitting laser structures on GaAs (311)B substrates by metalorganic chemical vapor deposition

Vertical-cavity surface-emitting laser (VCSEL) structures have been grown on GaAs (311)B substrates by metalorganic chemical vapor deposition. C-doped GaAs and AlAs layers with smooth surface morphology and a hole concentration of 1018 cm−3 were obtained by optimizing the growth conditions; these conditions contributed to high-quality p-type distributed Bragg reflectors (DBRs). The devices on the (311)B substrates exhibited a threshold current of 9.6 mA, voltage of 2.1 V, and maximum power of 4.1 mW at a 20 μm φ size; these characteristics are similar to those obtained on (100) substrates. The polarization was aligned to [2̄33̄].

Alternating Be and C doping for strain compensated GaAs/AlAs distributed Bragg reflectors

We demonstrate a new type of strain compensated, p-type distributed Bragg reflector (DBR) using alternating doping of Be in GaAs and C in AlAs with carbon concentrations as high as 2×1020 cm−3. These DBRs exhibit simultaneously a high crystalline quality, an excellent surface morphology, and no misfit dislocations, which cannot be achieved in undoped or Be-doped DBRs. The absolute optical reflectivity is as high as in the undoped DBR. The differential resistance of these structures is comparable to best reported values in Be-doped DBRs.