Abstract
The advent of high-speed Internet has seen renewed interest in fiber to the home (FTTH) systems due to the potentially greater economic revenues. Nowadays, the deployment of optical networks in long-haul networks has been promoted into SONET OC-192 (10 Gbit/S) standard for enhancing data transmission capacity and the technical development of diode lasers focuses on low cost and compact-size integration technology. In general, the performance of these conventional InGaAsP/InP 1.3 and 1.55 µm wavelength laser diode is limited by: (1) leakage currents especially at elevated temperatures; (2) thermal saturation; (3) long-term reliability; and (4) the strongly temperature-dependent optical gain and loss in the InGaAsP/InP material. There are two alternative methods to promote the structure and the performance of narrow-stripe InP-based lasers for wide temperature range application: the buried heterostructures (BH) and selective area metalorganic vapor phase epitaxy technique. In this dissertation we first describe the InGaAsP BH laser diodes fabricated by single-step MOCVD regrowth and self-aligned technique. A simple method to fabricate the high performance 1.55-μm InGaAsP/InP BH LDs with an intrinsic InP current blocking layer by single-step MOCVD regrowth and self-aligned technique. The method provides a high uniformity and high reproducibility of LD fabrication on a large size wafer. The BH LDs were buried by the intrinsic InP layer which used as the current blocking layer as well as a carrier and optical confinement layer and have a calculated internal quantum efficiency of 81%, an internal loss of 21.5 cm-1. With an as-cleaved front facet and a high reflectivity coating (~92%) was applied to the rear facet. The threshold current of BH LDs can be reduced to 3.4 mA at 20℃, 19 mA at 100℃, an increase of maximum operation temperature up to 125℃, and a characteristic temperature of 72 K in 20-60℃. The BH LDs with an as-cleaved front facet and a high reflectivity coating (~92%) applied to the rear facet can increase the maximum operation temperature up to 125℃ and have a light output power exceeded 10 mW at 80 mA and 100℃. These LD characteristics are comparable to those BH LDs with conventionally Fe-doped or p/n/p InP embedding layers as the current-blocking structure. In chapter 5, we next demonstrate the excellent index-guided 1.3 μm InGaAsP strain-compensated multi-quantum- well BH LDs grown by selective area metalorganic chemical vapor epitaxty (SA-MOCVD) on a patterned InP substrate. The photoluminescence (PL) of SCMQW active region grown on the patterned grooves has a narrow full width at half maximum of ~47 meV. These LDs grown on a patterned InP substrate show a low threshold current of 6.8 mA and a high light output power of 30 mW at 80 mA, a high slope quantum efficiency of 0.45 mW/mA, and a maximum operating temperature is 120℃with a characteristic temperature of 72 K in 20-80℃. The 3-dB modulation bandwidth of these LDs can be extended as far as 11.4 GHz under a bias level of 40 mA, and back-to-back test show a clear and symmetric eye diagram at 10 Gb/s with PRBS of 231-1 word length and a peak-to-peak voltage of 1.08 V at 85℃. From the accelerated aging test, the median lifetime for the LDs operating at 85℃ and 5mW is estimated to be longer than 9 x 104 hrs or 10 years. Throughout the chapter 6, we highlight performance advantages of 1.3-µm complex-coupled distributed feedback (CC-DFB) buried heterostructure (BH) laser diodes (LDs) with Fe-doped InGaAsP/InP hybrid grating layers. High optical coupling coefficient and eminent current confining ability are accomplished by combining the Fe-doped InGaAsP/InP current-blocking-grating (CBG) layers to provide both the index and gain distributed-feedback coupling coefficients. Besides, the narrow-stripe BH LDs are implemented by burying the active region with a Fe-doped InP current-blocking layer during the epitaxial regrowth. The fabricated CBG CC-DFB BH LDs at 20℃ shows a low threshold current of 5.3 mA, a maximum light output power of 36 mW at 100 mA, a high slope efficiency of 0.41 mW/mA. In addition, these LDs exhibit a maximum operation temperature of 125℃, an extremely low threshold current of 15.8 mA at 90℃, a small variation in slope efficient of only -1 dB at the temperature increased from 20 to 80℃, and a characteristic temperature of 70 and 58 K between 20 and 70℃ and 70 and 120℃, respectively. The LDs measured at a drive current of 2 × Ith exhibits a SMSR of approximately 42 dB at 10.5 mA, and increases to 45 dB above 15 mA, and stay stably in the same DFB mode with a high SMSR even at high temperatures. The analysis of wavelength shift with injected current demonstrates that the thermal dissipation capability of CBG CC-DFB BH LDs increases about 18%, which is attributed to the low thermal impedance of the Fe-doped InP buried layer. Furthermore, these 1.3 μm CBG CC-DFB BH LDs exhibit a high-speed characteristic up to 11.8 GHz at room temperature and an estimated median lifetime of more than 1.1 × 105 hrs or 12.5 years at 5 mW and 85℃. These excellent characteristics at high temperatures are achieved and the laser is expected to be well suited for 10-gigabit Ethernet applications.