Monolithic integration of microlensed resonant photodetectors andvertical cavity lasers

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 μA threshold currents. Adjacent detectors have the same operating wavelength and responsivities of ~0.4 A/W with ~6 nm optical bandwidths     

A comparative study of strain relaxation effects on the performanceof InGaAs quantum-well-based heterojunction phototransistors

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±15% from 950-970 nm, for 10 μW 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 (<10%) had no significant detrimental effects, allowing a large improvement in HPT performance. More heavily relaxed HPTs showed a degradation in both the inherent photodetector and transistor action, though this was not catastrophic in nature. A simple simulation of the results is carried out, suggesting that the dislocations adversely effect the carrier transport across the collector region, and also reduce the minority carrier diffusion length in the base     

Partially relaxed multiquantum well InGaAs/AlGaAs heterojunctionphototransistor operating at 955-970 nm

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     

High gain resonant cavity enhanced InGaAs/AlGaAs heterojunctionphototransistor resonant at 930 nm

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 μW incident optical power to 400 A/W at 100 μW     

Flip-chip bonded arrays of monolithically integrated, microlensedvertical-cavity lasers and resonant photodetectors

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 μA 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     

Densely packed pie shaped vertical-cavity surface-emitting laserarray incorporating a tapered one-dimensional wet oxidation

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 μm 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     

Resonant cavity-enhanced InGaAs-AlGaAs heterojunctionphototransistors with an optical design for high uniformity and yield

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%±1% of the incident optical power, even at wafer nonuniformities of 12.5%. With these nonuniformities, the resonant wavelength moves ±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 ±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 ±10% of the average responsivity     

Critical Dissolution Tests of Oral Systems Based on Statistically Designed Experiments. I. Screening of Critical Fluids and in Vitro/In Vivo Modelling of Extended Release Coated Spheres

Different compositions of in vitro dissolution fluids have been developed and used in screening experiments during the development of ethylcellulose ER-coated spheres of the model drug remoxipride. The composititons were different with respect to pH, temperature, osmotic pressure, viscosity, agitation, ionic strength, polarity of the medium, type, and concentration of surfactant. By using a chemometric methodology all the variables were varied independently at the same time, and the results were connected in a mathematical model which described the experimental domain. The most signifcant main effects on the amount of remoxipride released at all timepoints were caused by polarity, temperature, and agitation. The mathematical model was used to predict the in vitro condititons that was best associated with the in vivo data, obtained afer administration of the formulation to sixteen volunteers. A verihing experiment showed a close connection between the predicted and experimental in vitro dissolution profile up to 4 hr, but thereafter (up to 24 hr) the projiles deviated. It is obvious that the conditions need to be further optimized. However, the present approach to stress oral dosage systems during the development phase seems very promising.     

Analysis of the performance of the capacitive displacementtransducer

An output signal from the capacitive displacement transducer has been mathematically modeled. Interest is focused on the importance of the spectral content of the signal in determining transducer performance. It has been shown that the phase-error due to the space harmonics of the capacitance between the receiving and transmitting electrodes always exhibits a ripple with the spatial frequency equal to the number of the transmitting electrodes. An analysis of the mathematical model suggests general rules of mechanical and electrical design that are necessary in order to create effective and viable devices with reduced measurement errors. In particular, a variety of the staircase functions with rapidly decreasing Fourier components can be applied as the driving supply. Another alternative is to combine a specially formed driving supply with low-pass filtering in the time domain. Experimental results for three different (four-, six-, and eight-phase) transducer systems confirm the validity of the model     

Monolithic integration of substrate input/output resonantphotodetectors and vertical-cavity lasers

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 μA while maintaining differential efficiencies above 50%. Larger multimode VCLs have differential efficiencies exceeding 70% with threshold currents of 0.5 mA