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A package-integrated, compact, low-cost, athermal wavelength locker is introduced. It uses a novel etalon material, Schnaelite, to reduce environmental temperature sensitivity well over an order of magnitude compared to commercially available fused silica based lockers. Thermo-optical properties of temperature insensitive etalons are presented. Results demonstrating frequency stability of devices incorporating Schnaelite etalon based discriminators show optical frequency shifts below 1 GHz for large changes in case and laser temperature. This enabling technology promotes future small form-factor, low power consumption, multichannel laser sources.

We present theoretical and experimental results on monolithically integrated through-the-substrate input/output vertical-cavity lasers (VCLs) and resonant photodetectors that are compatible with substrate-side micro optics and flip-chip bonding. The required difference in bottom mirror reflectivity between the VCL and the detector is achieved by selective oxidation of a few high Al-content AlGaAs layers in the bottom mirror for the VCL. The modeling shows that using this approach makes it possible to individually design VCLs and resonant detectors from the same epitaxial structure without compromising performance of either device. Furthermore, since the oxidized layers are placed far enough from the active region, the VCL design is very robust with respect to uncertainties in the oxidized layers. For the detectors, we expect about 60% quantum efficiency, a 6-nm full-width at half-maximum optical bandwidth, and less than 1 nm difference in operating wavelength from the VCLs. Experimentally, VCLs and adjacent detectors with integrated microlenses have a difference of less than 0.5 nm in operating wavelength. The detectors have responsivities of 0.48 A/W, corresponding to 60% quantum efficiency and 7-nm optical bandwidths. Single-mode VCL's exhibit threshold currents as low as 135 /spl mu/A while maintaining differential efficiencies above 50%. Larger multimode VCLs have differential efficiencies exceeding 70% with threshold currents of 0.5 mA.

We present temperature, modulation, and free-space link characteristics of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The devices have been integrated using a novel structure that makes it possible to fabricate devices with through-the-substrate emission and detection. Taking advantage of the substrate emitting/detecting architecture, we monolithically integrate microlenses on the substrate side of the devices and flip-chip bond arrays without via processes or substrate removal. Low-threshold high-efficiency VCLs exhibit maximum small-signal modulation bandwidths, which are limited by parasitics, of /spl sim/9.5 GHz at 20/spl deg/C and /spl sim/8.4 GHz at 70/spl deg/C. The VCLs have the lowest reported bias currents required to reach bandwidths of up to /spl sim/8 GHz. A free-space optical link is demonstrated with flip-chip-bonded arrays of microlensed, monolithically integrated VCLs and detectors. The link is found to be tolerant to temperature differences of /spl plusmn/75/spl deg/C between the VCL and detector, with error free (BER

We have studied time-resolved cathodoluminescence (CL) and electron beam induced current (EBIC) on AlGaAs/GaAs/InGaAs heterojunction phototransistors under operating conditions, i.e., at room temperature and under bias. Devices from four wafers, with a different amount of lattice relaxation, were tested. It is shown that the CL intensity increases more than one order of magnitude as the voltage is increased and the current gain of the device turns on. The voltage dependence of the CL signal is analogous to the current–voltage curve of the transistor. The buildup in CL intensity was found to be much less in devices with low current gain showing that the CL intensity correlates to the electrical gain of the device. Time resolved CL showed two distinct CL decay times, one very short, a few nanoseconds, and one long, of the order of microseconds. This indicates that two fundamental recombination processes are present, which we attribute to a spatially direct recombination between carriers in the base and a sp...

The performance of a GaAs based heterojunction phototransistors (HPTs) using an n-p-i-n configuration, where the absorption is provided by InGaAs quantum wells (QWs) have been studied. Structures with differing numbers of QW were investigated. This allowed the tradeoff between the benefits of increased light absorption and the drawbacks of increased lattice relaxation, caused by the mis-match between InGaAs and the GaAs substrate, to be examined. All the HPT's investigated showed responsivities (A/W) far larger than unity, as well as large wavelength tolerance, for example 44 A/W/spl plusmn/15% from 950-970 nm, for 10 /spl mu/W incident optical. Electrical common-emitter current gains, of up to 3000 were measured for our HPT's and then confirmed by subsequent HBT measurements. Small relaxation levels (

We present uniformity data on resonant cavity-enhanced InGaAs-AlGaAs heterojunction phototransistors (HPT's) with an optical design that promotes high uniformity and yield. The HPT's operate in the wavelength region where the GaAs substrate is transparent and the data show the HPT's to be suitable for vertical integration with optical emitters or modulators to form two-dimensional arrays of smart pixels operating in transmission mode. The absorbing region of the HPT consists of an InGaAs multiple-quantum-well structure where the quantum wells (QW's) have been distributed to make the total absorption in the cavity insensitive to growth variations as well as the spatial matching of the standing wave and absorbing QW's. Theoretically, we estimate the absorption to be 39%/spl plusmn/1% of the incident optical power, even at wafer nonuniformities of 12.5%. With these nonuniformities, the resonant wavelength moves /spl plusmn/25 nm, making postgrowth tuning of the wavelength necessary. Experimentally, we show postgrowth tuning of the resonance wavelength without loss in uniformity. The arrays have good uniformity as well as very high responsivities. The average responsivity is 160 A/W /spl plusmn/15% from 927-955 nm. The standard deviation of a typical array is 0.5 nm in resonant wavelength and about 5% of the average responsivity. The difference between maximum and minimum values for an array is typically 3 nm in resonant wavelength and /spl plusmn/10% of the average responsivity.

We have studied the influence of structural defects on the spatial variation of radiative and nonradiative recombination in an InGaAs/AlGaAs/GaAs resonant cavity enhanced npn heterojunction phototransistor (HPT) structure using cathodoluminescence (CL) and electron beam‐induced current (EBIC) imaging. Absorber layers of InGaAs/GaAs multiple quantum wells (MQWs) are used to provide the photosensitivity for light with wavelengths that are transparent to the GaAs substrate. The current gain of the HPT under an applied bias voltage depends on the hole accumulation efficiency in the base and therefore on the hole lifetime. Strain relaxation‐induced misfit dislocations in the MQWs are found to create regions of enhanced nonradiative recombination thereby reducing locally the hole accumulation efficiency and current gain. The reduction in the local EBIC signal caused by the dark line defects is less than ∼20%, suggesting that misfit dislocations in this sample have a relatively small impact on overall device per...

We have theoretically and experimentally investigated the optical-excitation-dependent carrier recombination lifetime in a periodically /spl delta/-doped InGaAs/GaAs multiple-quantum-well structure. The spatial separation of photogenerated electrons and holes results in an increased sensitivity to the optical excitation intensity in proportion to the increase in carrier lifetime. Experimentally, we find more than six orders of magnitude reduction in the carrier recombination rate over that for spatially direct transitions under low-excitation conditions. On the other hand, theory predicts intrinsic recombination rates for ideal structures far below those found experimentally. Various mechanisms such as electric-field-enhanced redistribution of the dopants during epitaxial growth, statistical variations in the separation of the dopants, and extrinsic recombination channels caused by misfit dislocations are discussed as possible origins for this discrepancy. >

Wavelength-division-multiplexing (WDM) photonic integrated emitter (PIE) vertical-cavity surface-emitting laser (VCSEL) arrays are fabricated using a post growth wet oxidation technique. High-density integration of WDM VCSEL arrays is possible by combining the technique of one-dimensional oxidation and large-scale tapered oxidation. Eight channels are integrated into a circle of 60 /spl mu/m in diameter. Seven channels are found to operate as lasers. The lasing wavelengths range from 823 to 836 nm corresponding with the distance between the VCSEL mesa and the tuning trench. The successful demonstration of incorporating wet oxidation into the wavelength control of the PIE VCSEL array opens a new way of fabricating mask-defined densely packed WDM VCSEL arrays.

Semiconductor lasers emitting at 1.55 μm with external differential efficiencies >1 have been created by monolithically connecting several active regions in series within a single optical waveguide. This is accomplished by epitaxially stacking a number of p–i–n multiquantum well active regions with intermediate n++–p++ back diodes, which enable the entire terminal current to flow through each active region stages in series. Such lasers should also improve the impedance match as well as provide for low-noise, high-efficiency microwave links.

We present flip-chip bonded arrays of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The VCLs and photodetectors are integrated using a novel structure that allows through-the-substrate emission and detection without compromising device performance. Substrate-side microlenses have been integrated to take advantage of the through-the-substrate architecture. Flip-chip bonded VCLs exhibit threshold currents as low as 135 /spl mu/A with differential efficiencies of /spl sim/53%. The detectors have the same operating wavelength as the VCLs and responsivities of 0.48 A/W, corresponding to 60% absorption, with optical bandwidths of 7 nm.

We demonstrate a design that allows fabrication of substrate input/output resonant-cavity photodetectors and vertical cavity lasers (VCLs) on the same substrate without regrowth. By selectively oxidizing a few layers in the bottom mirror the as-grown 80% reflectivitymirror, used as the input mirror for the detector, is converted to a 99.3% reflectivitymirror allowing fabrication of VCLs from the same epitaxialmaterial. Since these two reflectivities are uncorrelated, the detectors and VCLs can be individually designed. Despite the change in refractive index from ∼3 to ∼1.6 in the oxidized layers, the structure can be designed to have nearly the same resonance wavelength for both the detectors and VCLs. Using this design strategy, we have successfully fabricated high-performance resonant photodetectors and VCLs from the same epitaxialmaterial. The photodetectors have an absorption of 56% and an optical bandwidth of 5.9 nm, in good agreement with theory. Small diameter, single-mode VCLs have threshold currents as low as 180 μA with 33% slope efficiencies while multimode devices have slope efficiencies exceeding 60% with less than 500 μA threshold currents.

We report on heterojunction phototransistors (HPTs) operating at GaAs substrate transparent wavelengths beyond 900 nm, utilizing a strained InGaAs quantum well based absorbing region. High performances have been measured with responsivities of ≊80 and 200 A/W at 10 and 50 μW, respectively. The results correspond to electrical current gains of up to 3000 for currents of ≊10 mA, the best reported results for such phototransistor structures. The effect of strain relaxation on device performance is examined, and it is seen that it can cause a degradation both in terms of the transistor and photodiode characteristics of the HPT.

We have studied the influence of misfit dislocations on hole accumulation in the base layer of an n‐AlGaAs/p‐GaAs/n‐InGaAs heterojunction phototransistor (HPT). Spatially and temporally resolved cathodoluminescence (CL) measurements reveal that variations in the hole accumulation is caused primarily by strain‐induced defects which impede the transport of holes in the collector. The lifetime of holes in the InGaAs/GaAs collector is found to be negligibly affected by the underlying misfit dislocations in the InGaAs/GaAs collector. The reduction in the local electron‐beam‐induced current signal by the dislocations is less than ∼20%, indicating that these defects have a minor impact on the overall device performance.

The development of vertical-cavity surface-emitting lasers (VCSELs) at the telecommunications important wavelength of 1.55 /spl mu/m has been hindered by the absence of a substrate that is suitable for both technologically-developed distributed Bragg reflectors (DBRs) and quantum well active regions. AlGaAsSb-based DBRs, however, which can be lattice-matched to InP and have a refractive index-contrast that is similar to AlGaAs-based DBRs at 1.3 /spl mu/m-1.55 /spl mu/m, offer the opportunity to combine the mature InP-based active region technology with high reflectivity mirrors in a single growth. We have recently reported, in fact, electrically-pumped, Sb-based vertical-cavity lasers operating at 1.55 /spl mu/m and produced in a single epitaxial growth. These lasers, which employ two n-type, lattice-matched AlGaAsSb mirrors and an AlInGaAs-based active region, had room temperature threshold current densities of 1.4 kA/cm/sup 2/ and an external quantum efficiency of /spl sim/18%. The VCSELs, unfortunately, suffered from a very high operating voltage. We present design changes that have significantly reduced this voltage and discuss future improvements that could lead to further reductions.

We have demonstrated electrically pumped operation at 1.55 /spl mu/m at room temperature of vertical-cavity lasers (VCLs) grown lattice-matched on InP. The VCLs present threshold currents lower than 10 mA. Powers around 10 mW and external quantum efficiencies of 38.3% have been measured.

We have demonstrated fully-epitaxial, room-temperature, electrically-pumped VCSELs based on III-As compounds with low threshold current density, very high differential efficiency and low threshold voltage by employing multiple-active-regions in a single cavity. Even higher differential efficiencies should be possible with optimized cavity designs. The high differential efficiency and high output powers makes these VCSELs good candidates for low-noise, high-efficiency microwave links. Also, when integrated with a series connected detector, analog repeaters, amplifying wavelength converters, and lossless signal tapping are possible.

We present flip-chip bonded arrays of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The VCLs and photodetectors are integrated using a novel structure that allows through-the-substrate emission and detection without compromising device performance. Substrate-side microlenses have been integrated to take advantage of the through-the-substrate architecture. Flip-chip bonded VCLs exhibit threshold currents as low as 135 /spl mu/A with differential efficiencies of 53%. The detectors have the same operating wavelength as the VCLs and responsivities of 0.48 A/W, corresponding to 60% absorption, with optical bandwidths of 7 nm. The VCLs exhibit maximum small-signal modulation bandwidths, which are limited by parasitics, of /spl sim/9.5 GHz at 20/spl deg/C and /spl sim/8.4 GHz at 70/spl deg/C. The VCLs have the lowest reported bias currents required to reach bandwidths of up to /spl sim/8 GHz. A free-space optical link is demonstrated with these flip-chip bonded arrays of microlensed, monolithically integrated VCLs and detectors. The link is found to be tolerant to temperature differences of /spl plusmn/75/spl deg/C between the VCL and detector, with error free (BER

Semiconductor lasers with external differential efficiencies >1 have been created by monolithically connecting several active regions in series within a single optical waveguide. In contrast to previous reports, we have accomplished this task at the technologically important 1.55 /spl mu/m wavelength. This is accomplished by epitaxially stacking a number of p-i-n multi-quantum well active regions with intermediate n/sup ++/p/sup ++/ back-diodes, which enable the entire terminal current to flow through each active region stage in series. In optimized structures, the stacking of N/sub A/ active regions should result in a multiplication of the external efficiency by N/sub A/ and a reduction of the threshold current by a factor a little less than N/sub A/, with only a slight increase in the threshold spontaneous emission power. Thus, the signal to noise ratio for modulated signals can be reduced. Such lasers should improve low-noise, high-efficiency microwave links and integrated detectors, analog repeaters, amplifying wavelength converters, and lossless signal are possible.

Semiconductor CW lasers with external differential efficiencies >1 have been created by monolithically connecting several active regions in series within a single optical waveguide. This task has been accomplished at the technologically important 1.55/spl mu/m wavelength. This is achieved by epitaxially stacking a number of p-i-n multi-quantum well active regions with intermediate n/sup ++/-p/sup ++/ back-diodes, which enable the entire terminal current to flow through each active region stage in series. Such lasers should also improve impedance match as well as provide for low-noise, high-efficiency microwave links.

A package-integrated, compact, low-cost, athermal wavelength locker uses a novel etalon material to reduce environmental temperature sensitivity >40x compared to commercially available materials. This enabling technology promotes small form-factor, low power consumption, multichannel laser sources.

Summary form only given. We demonstrate a novel design that allows the fabrication of photodetectors and vertical-cavity lasers with integrated microlenses from a single epitaxial growth by selective oxidation of the bottom mirror.

We present the first monolithic integration, without regrowth, of high-performance substrate input/output vertical-cavity lasers (VCLs) and resonant photodetectors that are compatible with flip-chip bonding and integrated microlenses. Integrated arrays of these devices are critical components for very dense bi-directional free-space optical interconnects. VCLs and resonant detectors fabricated side-by-side on the same chip have the same wavelength of operation to within

We present flip-chip bonded arrays of novel, monolithically integrated, microlensed vertical-cavity lasers (VCLs) and resonant photodetectors. The bottom emitting VCLs exhibit ∼300 μA threshold currents, while adjacent detectors have the same operating wavelength and responsivities of ∼0.4 A/W. Only a single epitaxial growth is required.

In conclusion we have presented an RCE-HPT heterojunction phototransistor with an MQW absorber that is tolerant to inhomogeneous and homogeneous variations in layer thicknesses. Arrays show good uniformity as well as record high responsivities. The standard deviation of a typical array is 1.1 nm in resonant wavelength and 13.3 A/W in peak responsivity. This is significantly smaller than the FWHM optical bandwidth of 7 nm and about 8% of the average peak responsivity of 163 A/W at 10 /spl mu/W optical input.

Summary form only given. Owing to their geometric advantage with respect to mass production, WDM VCSEL arrays have drawn attention as a low cost means of increasing data transmission rate for short haul communications. Recently, pie-shaped WDM VCSEL arrays were successfully fabricated by means of anodic etching followed by regrowth. In addition to this work, wavelength tuning of VCSEL emission has been demonstrated via postgrowth oxidation. In this paper, we present the results of applying postgrowth oxidation to the fabrication of mask-defined densely-packed WDM VCSEL arrays.

The development of monolithic 1.55 /spl mu/m VCSELs has been hampered by the lack of readily available highly reflective DBRs. However, it is possible to achieve lasing with less reflective DBRs by epitaxially stacking multiple active regions and increasing the gain. For example, 30.5-period AlGaInAs/AlInAs DBRs can be mated to a three-stage active region to achieve lasing. Epitaxy of such VCSEL can be short enough to maintain source stability in an MBE system. The other benefit is greater differential efficiency, which can actually exceed unity, for greater signal to noise ratio. We have investigated the properties of such active regions. We have created edge-emitters with external differential efficiencies >1 by monolithically connecting several active regions in series within a single optical waveguide. In contrast to previous reports, we have accomplished this task at the technologically important 1.55 /spl mu/m wavelength.

A free-space optical link is demonstrated using monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The devices have been integrated using a novel epitaxial structure that makes it possible to fabricate devices with through-the-substrate emission and detection using only post-growth processing [1].

The excitation dependent carrier recombination lifetime in periodically (delta) -doped strained InGaAs/GaAs multiple quantum well structures has been investigated both experimentally and theoretically. Experimentally, we find more than six orders of magnitude increase in the lifetime over that for undoped material due to the spatial separation of photogenerated carriers. This results in strong photo-optic effects and optical nonlinearities. Calculations, on the other hand, predict intrinsic recombination lifetimes in the periodically (delta) -doped material far above those found experimentally. Using secondary ion mass spectroscopy, transmission electron microscopy, cathodoluminescence imaging, and electron beam induced absorption modulation imaging we find evidence for misfit dislocation related recombination mechanisms that limit the carrier lifetime in the strained quantum well material.

The authors report a partially relaxed InGaAs multiquantum well based heterojunction phototransistor with high responsivity in the transmission window of the GaAs substrate which shows no degradation in performance due to lattice relaxation. The peak responsivity increased from 10 A/W at 0.5 µW incident optical power to 100 A/W at 50 µW, corresponding to a current gain of 925. At 8 V collector-emitter voltage the responsivity is constant from 957 to 973 nm, with a responsivity of 5 A/W at 0.5 µW and 55 A/W at 50 µW.

A resonant cavity enhanced InGaAs/AlGaAs phototransistor with high responsivity in the transmission window of the GaAs substrate is reported. The resonant wavelength is 929 nm with a full width at half maximum of 9 nm. The peak responsivity increases from 17 A/W at 0.1 mu W incident optical power to 400 A/W at 100 mu W.

The molecular beam epitaxy and the characterization of single-step grown long wavelength vertical cavity surface emitting lasers (LW–VCSEL) are reported. The devices were fabricated using highly reflective AlGaAsSb/AlAsSb distributed Bragg reflectors (DBRs), and an AlGaInAs-based active region embedding a tunnel (or Esaki) junction. The VCSELs operate at 1.55 μm at room temperature with a threshold current density of 1.4 kA/cm2. Characterization of the VCSELs and DBRs’ thermal and electrical properties is presented. Major improvement on the voltage drop in an InGaAs capped DBR is demonstrated, resulting in a value as low as 40 mV/pair.

Electrically-pumped, Sb-based vertical-cavity lasers operating at 1.55 µm and produced in a single epitaxial growth have been demonstrated. These lasers, which employ AlGaAsSb mirrors and an AlInGaAs-based active region, have room temperature threshold current densities of 1.4 kA/cm2 and an external quantum efficiency of ~18%.

Monolithic integration of high performance microlensed resonant photodetectors and vertical cavity lasers (VCLs) from a single epitaxial growth is presented. The VCLs have sub-200 /spl mu/A threshold currents. Adjacent detectors have the same operating wavelength and responsivities of /spl sim/0.4 A/W with /spl sim/6 nm optical bandwidths.

The optical crosstalk between lasers in densely-packed multiple-wavelength vertical-cavity photonic integrated emitter arrays is studied for multimode wavelength-division multiplexing applications. It is found that a significant number of photocarriers are generated by spontaneous emission of an adjacent laser. However, an appropriate prebiasing scheme or device design can reduce the crosstalk to < –20 dB.