Investigation of GaAs-based Long Wavelength Lasers and Photodetectors Grown by MOVPE

• Main Authors: Wei-Cheng Chen, 陳威呈
• Other Authors: Yan-Kuin Su
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/75332761081046066252

博士 === 國立成功大學 === 微電子工程研究所碩博士班 === 96 === The main purpose of the dissertation is to develop the GaAs-based materials, such as including the highly strained InGaAs/GaAs, InGaAsN/GaAs and type II GaAsSb/GaAs quantum wells (QWs) which are capable of delivering long wavelength operations. The growth conditions, optical properties, and devices characteristics are systematically studied. After optimizing the epitaxial parameters, the InGaAs/GaAs lasers were continuous-wave (CW) operated at 1.22 μm under extremely low threshold current density (Jth) ~ 140 A/cm2 (Jth/QW = 46.7 A/cm2/well). The demonstrated InGaAs QW laser has the lowest transparent current density (Jtr) and among the reported InGaAs lasers longer than 1200nm. The characteristic temperature of 146.2K thus obtained indicates the excellent temperature characteristics and good electron confinement. In addition, the high quality InGaAs/GaAs QW grown under low temperature and TBAs/III ratio also provides a good starting point for the InGaAsN alloys by MOVPE. To extend the emission wavelength, the dilute-nitride alloys -InGaAsN grown by MOVPE were studied. Using low temperature, moderate growth rate, high DMHy/V ratio and low indium composition would enhance nitrogen incorporation. Besides, the DMHy/V ratio was adjusted by altering TBAs flows only to avoid the parasitic reaction between TEGa and DMHy, which eventually led to stable control of indium composition and growth rates of InGaAsN layer. After optimizing the growth parameters and thermal annealing conditions, the PL intensity of InGaAsN/GaAs DQWs was improved by almost 10 times. The InGaAsN edge-emitting lasers were fabricated and showed very good temperature characteristics. The 1.3 μm operation was realized, and the emission wavelength was 1314.52nm. However, the Jth was as high as 1.5 KA/cm2, and still need to be further reduced for actual application. Optimizing InGaAsN alloys via the use of purified nitrogen precursor, and applying the Sb surfactant effect could improve the optical properties of InGaAsN/GaAs lasers. By using the TMSb surfactant flow, the PL peak intensity and FWHM of InGaAsN/GaAs QWs were both improved. The localization effect was suppressed by introducing the TMSb flow before growing the InGaAsN layer. Furthermore, the aluminum issues of InGaAsN were resolved by the Sb surfactant. The origin of this improvement was attributed to the better crystal quality and lower surface roughness of the Sb-treated samples. The aforementioned advantages demonstrated that the Sb surfactant could be a very effective way to improve the optical properties of InGaAsN layer, enabling the realization of the InGaAsN lasers of low threshold current density grown by MOVPE. The other high strained QWs, such as GaAsSb/GaAs, were also proposed as possible device structures for long wavelength lasers. The growth conditions and optical properties of GaAsSb alloys were systematically studied. Lowering the AsH3/III ratio and increasing growth temperature to 610 oC could increase the Sb incorporation of GaAsSb. High TMSb flow rate would reduce Sb composition, suppress the growth rate and deteriorate the interface quality due the excess Sb coverage on GaAs surface. The highest Sb composition of GaAsSb obtained was as high as 0.32 and the longest PL wavelength achieved was 1273nm, limited by our MOVPE system design. Therefore, the GaAsSb/InGaAs bi-layer structures were proposed, which showed a longer wavelength at 1295nm with moderate PL intensity. Lastly, two GaAsSb/GaAs DQWs edge-emitting lasers were fabricated. The lasing peaks were 1130 and 1203nm, and these two different diode lasers demonstrated high characteristic temperature of 146K and 130K. To our knowledge, the lasing wavelength and the T0 of the GaAsSb/GaAs DQWs laser are among the best results of GaAsSb/GaAs lasers grown by MOVPE. Furthermore, the radio frequency (RF)-sputtered indium-tin-oxide (ITO) layers as the transparent contact layer of the metal-semiconductor-metal (MSM) photodetectors (PDs) were studied. The metal-insulator-metal-semiconductor (MIMS) has the highest photo/dark current ratio of 45.29 under 0.5 V bias for the much improved surface roughness between the SiO2 layer and the InGaAsN bulk. Further improvements on the material quality of InGaAsN layers, an increase in the absorption layer thickness, and the use of AR-coating were necessary to obtain higher responsivity and quantum efficiency. Despite the higher threshold current density of InGaAsN and GaAsSb QW lasers, the foregoing GaAs-based lasers thus demonstrated have good temperature characteristics, and are also capable of delivering 1.3 μm operation. In conclusion, the GaAs-based materials are experimentally proved as suitable candidates for replacing the conventional InP-based lasers.