V. Swaminathan

Effect of p-doping profile on performance of strained multi-quantum-well InGaAsP-InP lasers

Leakage of electrons from the active region of InGaAsP-InP laser heterostructures with different profiles of acceptor doping was measured by a purely electrical technique together with the device threshold current. Comparison of the obtained results with modeling data and SIMS analysis shows that carrier leakage of electrons over the heterobarrier depends strongly on the profile of p-doping and level of injection. In the case of a structure with an undoped p-cladding/waveguide interface, the value of electron leakage current can reach 20% of the total pumping current at an injection current density of 10 kA/cm at 50/spl deg/C. It is shown that carrier leakage in InGaAsP-InP multi-quantum-well lasers can be minimized and the device performance improved by utilizing a p-doped separate-confinement-heterostructure layer.

Zn diffusion behavior in InGaAsP/InP capped mesa buried heterostructures

A systematic study of the effects of Zn doping and diffusion in InGaAsP/InP capped mesa buried heterostructure lasers grown by metalorganic chemical vapor deposition was carried out. It consisted of varying the Zn doping of the p‐InP cladding layer in the base epitaxial structure over the range (0.7–3.1)×1018 cm−3 and keeping the growth conditions in two subsequent regrowth steps the same. Secondary ion mass spectrometry was employed for a quantitative determination of the Zn depth profiles following regrowth using test sites on the 50 mm round wafers that contained the appropriate epitaxial layers. Clear evidence of Zn diffusion such as the penetration of Zn into the active layer and the presence of inflection points (accumulation and depletion of Zn near the p‐n heterojunction) was illustrated in the depth profiles. It was observed that the diffusion of Zn during the third growth dominated the Zn profile in the base growth part of the p‐InP layer and the final amount of Zn in this region was independent...

Electron cyclotron resonance plasma‐induced damage in AlGaAs/GaAs/AlGaAs single quantum wells

Changes in cathodoluminescence (CL) intensity from a buried single AlGaAs/GaAs/AlGaAs quantum well (QW) as a result of exposure to electron cyclotron resonance (ECR) hydrogen or argon discharges are reported. For additional dc biases of 150 V on the sample during either H2 or Ar plasma exposure, we observe substantial decreases in CL intensity from the well. Ar+ ion bombardment creates damage more resistant to annealing than does H+ ion bombardment at the same energy. The ECR discharges alone with zero additional dc bias cause degradation in the well luminescence due possibly to defects created by energetic electron bombardment or ultraviolet illumination. At intermediate bias voltages (50 V) strong hydrogen passivation of nonradiative centers is observed, leading to 500% increases in CL intensity from the well. The initial characteristics of the QW under these conditions are restored by annealing at 400 °C.

Unintentional zinc diffusion in InP pn-homojunctions

Unintentional zinc diffusion into uniformly Si-doped InP layers has been studied. The sharp non-error function Zn concentration profiles and inflections are shown to be consistent with the substitutional-interstitial mechanism when the influence of the electrostatic field of the pn-junction on diffusion is taken into consideration.

Hydrogen passivation of Si δ-doped GaAs grown by molecular beam epitaxy

Hydrogen passivation of Si δ‐doped GaAs grown by molecular beam epitaxy is studied. Just as in uniformily Si‐doped GaAs, exposure of the δ‐doped material to a low frequency (30 kHz) hydrogen plasma at 250 °C for 30 min deactivates the Si donors in the δ spikes. For samples with Si doping of (1–6)×1018 cm−3, carrier concentration in the spikes decreased by nearly three orders of magnitude following hydrogenation. Secondary‐ion mass spectrometric analysis of deuterated samples confirmed trapping of deuterium in the Si‐doped spikes. Consistent with the deactivation of Si donors following hydrogenation, changes were observed in the near‐band edge luminescence spectrum at 4.2 K, which showed in the hydrogenated sample the absence of Burstein–Moss shift that was observed in the as‐grown sample. This hydrogen‐induced passivation of Si donors in the δ spikes can be of benefit in selectively deactivating donor atoms in device applications, and also provide a method for tailoring the hydrogen distribution in an epi...

Ambipolar lifetimes in GaAs/AlGaAs self-electro-optic-effect devices

We have used an electrical technique to determine the ambipolar lifetime in p‐i‐n GaAs/AlGaAs self‐electro‐optic‐effect devices in which the i region consists of a multiple quantum well structure (MQW). From an analysis of the voltage drop in the i region obtained from the forward current‐voltage characteristics, values for the ambipolar lifetimes are derived for diodes with different MQW. A value of 80–90 ps is determined for the ambipolar lifetime which is found not to change significantly when the AlxGa1−xAs barrier thickness or composition is reduced from 65 to 35 A or x∼0.3 to 0.2, respectively, in the MQW. Since these changes in the barrier have previously been shown to improve photoresponse efficiency of the p‐i‐n diode, it is inferred that the carrier escape and collection times are smaller than 80–90 ps in devices with thin (35 A) or low (x∼0.2) AlxGa1−xAs barrier.

Structural and optical properties of strained In0.2Ga0.8As-GaAs quantum wells

We report on Molecular Beam Epitaxial growth and properties of strained In0.2Ga0.8As-GaAs quantum well (QW) structures suitable for 980 nm lasers. The QW width was maintained at 80 A and the barrier thickness was varied from 50 A to 300 A. The effects of increasing the barrier width on the structural and optical properties of the QW were examined using double crystal x-ray diffraction rocking scans (DCXRD) and photoluminescence measurements. DCXRD rocking scans revealed satellite peaks from the strained layer quantum wells (SLQW). The linewidth of the peaks decreased as the barrier width was increased. Optical measurements indicate significant improvements in the internal luminescence efficiency in the thick barrier structures. We assign the improvements in the luminescence properties to the reduction of non-radiative centers in the thick barrier structures. The sources of the non-radiative centers are ascribed to structural defects that are generated as a result of strain relaxation in the thin barrier structures. A new broad photoluminescence feature at 0.9 eV was also observed and believed to originate in the AlGaAs:Si cladding region. We shall present these results and discuss the implications of increasing the barrier thickness of In0.2Ga0.8As-GaAs QW on the performance of 980 nm lasers.

Producibility of GaAs quantum-well infrared photodetector arrays

We discuss in detail the producibility issues associated with GaAs/AlxGa1-xAs quantum well infrared photodetectors (QWIPs). Excellent uniformity in growth (thickness, doping, and Al concentration) and in processing are expected to lead to high yield, high performance large area infrared imaging arrays.

High-power, high-efficiency, and highly uniform 1.3-um uncooled InGaAsP/InP strained multiquantum-well lasers

In order to meet the increasing market needs for uncooled lasers for such applications as fiber- in-the-loop, high efficiency, high power, and highly reliable 1.3 micrometer uncooled InGaAsP/InP strained multi-quantum well Fabry-Perot lasers were fabricated with 50 mm wafer processing. Slope efficiency as high as 0.39 W/A and peak power as high as 46 mW at 85 degrees Celsius was obtained by optimizing the device structure for high temperature operation. We have also demonstrated excellent uniformity and reproducibility over 6 wafers. Reliability was also shown to be very good. More than 10,000 chips sites are available on a 50 mm wafer, and the cost is expected to be low. Because of the high performance, these lasers are expected to be used for various applications.

Effect of p-doping profile on performance of strained multiquantum well InGaAsP/InP lasers

Leakage of electrons from the active region of InGaAs/InP laser heterostructures with different profiles of acceptor doping was measured by a purely electrical technique together with the device threshold current. Comparison of the obtained results with modeling data and SIMS analysis shows that carrier leakage of electrons over the heterobarrier depends strongly on the profile of p-doping and level of injection. In the case of a structure with an undoped p- cladding/waveguide interface the value of electron leakage current can reach 20% of the total pumping current at an injection current density of 10 kA/cm2 at 50 C. It is shown that carrier leakage in InGaAsP/InP multi-quantum-well lasers can be minimized and the device performance improved by utilizing a p-doped SCH layer.