R. L. Brown

Pt/Ti/p‐In0.53Ga0.47As low‐resistance nonalloyed ohmic contact formed by rapid thermal processing

Very low resistance nonalloyed ohmic contacts of Pt/Ti to 1.5×1019 cm−3 Zn‐doped In0.53Ga0.47As have been formed by rapid thermal processing. These contacts were ohmic as deposited with a specific contact resistance value of 3.0×10−4 Ω cm2. Cross‐sectional transmission electron microscopy showed a very limited interfacial reacted layer (20 nm thick) between the Ti and the InGaAs as a result of heating at 450 °C for 30 s. The interfacial layer contained mostly InAs and a small portion of other five binary phases. Heating at 500 °C or higher temperatures resulted in an extensive interaction and degradation of the contact. The contact formed at 450 °C, 30 s exhibited tensile stress of 5.6×109 dyne cm−2 at the Ti/Pt bilayer, but the metal adhesion remained strong. Rapid thermal processing at 450 °C for 30 s decreased the specific contact resistance to a minimum with an extremely low value of 3.4×10−8 Ω cm2 (0.08 Ω mm), which is very close to the theoretical prediction.

High‐output power InGaAsP (λ=1.3 μm) strip‐buried heterostructure lasers

An InGaAsP (λ=1.3 μm) strip‐buried heterostructure laser with active layer strip widths of 5 μm is described. These devices show stable fundamental‐transverse‐mode operation with linear light‐current characteristics to pulsed output powers over 100 mW. Output powers as high as 500 mW are observed without catastrophic damage, which corresponds to twice the power output at which catastrophic mirror damage occurs for similar GaAlAs SBH lasers. Far‐field beam divergence is approximately 10° and 30° in the directions parallel and perpendicular to the junction, respectively. cw operation with a threshold current of 170 mA has been achieved at room temperature.

Electronically tunable distributed feedback lasers

The fabrication and performance characteristics of frequency tunable two‐section distributed feedback lasers are reported. The lasers are of the double channel planar buried heterostructure type and utilize a second order grating for frequency selective feedback. The laser emits in a single frequency with a cw linewidth of ∼50 MHz. The single frequency output can be tuned by ∼2 A by varying the current through one of the two sections. Electronically tunable sources of this type are potentially useful for coherent fiber transmission systems.

Pt/Ti/p‐InGaAsP nonalloyed ohmic contact formed by rapid thermal processing

Nonalloyed ohmic contacts of Pt/Ti to 5×1018 cm−3 doped p‐InGaAsP (λg =1.3 μm) have been fabricated by rapid thermal processing of sputtered and e‐gun‐deposited metallizations. While the former as‐deposited had a rectifying characteristic, the latter showed ohmic behavior prior to any heat treatment, with a specific contact resistance of 4×10−3 Ω cm2. Rapid thermal processing at temperatures higher than 400 °C caused the formation of ohmic contacts for the sputtered metals also, but with the evaporated metals producing slightly lower contact resistance. The lowest specific contact resistance values of 3.6–5.5×10−4 Ω cm2 for evaporated and sputtered metallizations, respectively, were achieved in both cases as a result of heating at 450 °C for 30 s. These heating conditions produced only a limited reaction at the Ti/InGaAsP interface, which was sharper for the e‐gun‐deposited contact, but had a significant effect on the stresses in the Ti/Pt bilayer. In both the sputtered and electron gun evaporated samples...

Integrated external cavity laser

The fabrication and performance characteristics of single frequency integrated external cavity lasers of the coupled cavity type and the distributed Bragg reflector type are described. The active cavity section of these devices utilizes the double channel planar buried heterostructure scheme for current confinement. The lasers emit near 1.55 μm. The threshold current of these lasers is in the range 70–120 mA. cw linewidth of 7 MHz has been obtained for a 2‐mm‐long laser at an output power of 3 mW. We believe lasers with longer external cavity should exhibit lower cw linewidths.

Stress compensation in GaAs–Al0.24 Ga0.76 As1−y Py LPE binary layers

To improve the performance and reliability of heterostructure GaAs lasers, it is important to reduce stress in the epitaxial layers caused by lattice mismatch between GaAs and AlxGa1−xAs. More precise measurements than previously available have been made on the lattice mismatch of binary layers of GaAs–Al0.24Ga0.76As1−yPy and GaAs–Al0.36Ga0.64As1−yPy from radius‐of‐curvature measurements. The heterostructures were grown by LPE, with various atom fractions of P, on (100) and (211) GaAs substrates. Liquidus values of P concentration at 780°C growth temperature to achieve room‐temperature lattice matching have been determined to ±4%. The threshold value of the lattice mismatch and layer thickness product on (211) substrates necessary to avoid misfit dislocations is given.

Monolithically integrated thermoelectric controlled laser diode

The fabrication and performance characteristics of a monolithically integrated thermoelectric controlled laser diode are described. The thermoelectric element is the n‐InP substrate. The lasers (λ∼1.51 μm InGaAsP) have threshold currents of ∼20 mA and operate kink free to >10 mW/facet. A variation of active region temperature of ± 2.5 °C has been achieved using 50 mA of thermoelectric controller current. The observed frequency tuning rate associated with this temperature shift is ∼0.5 GHz/mA. The device is useful for applications that require a high degree of frequency stability or small frequency tuning. Some potential lightwave system applications are in single‐frequency transmission systems, coherent transmission systems, optical amplifiers, resonant external cavity modulators, and injection locking.

Fabrication and performance characteristics of InGaAsP multiquantum well double channel planar buried heterostructure lasers

We report the fabrication and performance characteristics of InGaAsP double channel planar buried heterostructure (DCPBH) lasers with multiquantum well active layers emitting at 1.3 μm. These lasers have threshold currents in the range 40–50 mA at 30 °C, external differential quantum efficiencies of ∼50% at 30 °C, and T0 values ∼160–180 K in the temperature range 10–60 °C. Under optical pumping the measured T0 are in the range 100–150 K. The lasers operate in a single transverse mode up to high powers (>10 mW/facet), can be modulated at ∼2 Gb/s, and exhibit less frequency chirping than similar lasers with conventional active layers. The observed high T0 and smaller chirp make DCPBH multiquantum well lasers potentially attractive for system applications.

Fabrication and performance characteristics of buried-facet optical amplifiers

The fabrication, performance characteristics, and design rules of buried-facet optical amplifiers are described. Chip gain of 25 dB, gain ripple of <1 dB, and gain difference of ≤1 dB for TE- and TM-polarized light are observed. The gain ripple and polarization dependence of gain correlate well with the ripple and polarization dependence of the amplified spontaneous emission spectrum. The performance of buried-facet amplifiers is comparable to that of cleaved-facet amplifiers with very good antireflection (R<10−4) coatings. The buried-facet design reduces the requirement on antireflection coatings and makes the fabrication process more reproducible.

High‐power gain‐guided InGaAsP laser array

We have fabricated InGaAsP gain‐guided laser arrays emitting at 1.3 μm. These devices have threshold currents in the range 300–400 mA at 30 °C and have been operated to pulsed output powers as high as 400 mW. More than 100 mW of output power has been obtained up to an ambient temperature of 60 °C. The lasers emit in multilongitudinal modes with a far‐field divergence of 20°×35°. A gain‐guided InGaAsP laser array of the type described here can be used in some applications requiring high‐power lasers emitting at 1.3 μm.