Residual stresses in sputtered ZnO films on Si are determined and discussed. By means of X-ray diffraction, we show that as-deposited ZnO films are highly compressively stressed. Moreover, a transition of stress is observed as a function of the post-deposition annealing temperature. After an 800°C annealing, ZnO films are tensily stressed while ZnO films encapsulated by Si3N4 are stress-free. With the aid of in-situ X-ray diffraction under ambient and argon atmosphere, we argue that this thermally activated stress relaxation may be attributed to a variation of the stoichiometry of the ZnO films.

Metal organic vapor phase epitaxy (MOVPE) growth conditions for the preparation of GaInAsN/GaAs single quantum wells (SQW) have been investigated using tertiarybutylarsine (TBAs) and dimethylhydrazine (DMHy) as arsenic and nitrogen precursors, respectively. We found that a low reactor pressure is required to minimize the effect of the DMHy injection on the indium composition of GaInAsN alloys. We have also established that a high TBAs/III ratio results in a significant improvement of the crystal quality GaInAsN/GaAs SQWs when it is combined with a low growth rate and a low growth temperature. As a result of such optimisation, the photoluminescence (PL) intensity of SQWs emitting at 1.3μm could be increased by one order of magnitude and the PL line width could be reduced by half compared with more standard conditions using a lower TBAs/III ratio. The lasing threshold of optimised GaInAsN lasers emitting at 1.24μm could be reduced by a factor of 6. We achieved photoluminescence emission at wavelengths up to 1.35μm and lasing at 1.26μm with a threshold as low as 540A/cm2 for a cavity length of 1220μm.

In this letter, we propose two new structures, the GaInAs-GaInNAs intermediate layer (IML) and the GaInNxAs graded wells, which show better optical properties than the commonly used GaInNAs-GaAs rectangular quantum-wells. A 1240-mn emitting IML laser has been achieved with a low-threshold current density (200 A/cm(2)/well) and a relatively high characteristic temperature (T-o = 100 K). The IML structure is very promising for long wavelength GaAs-based laser applications.

GaInAsN material grown on GaAs substrate have received a large amount of interest for several years as an alternative material system to the well matured GaInAsP/InP semiconductor system, especially for 1.3 μm emission. However, a specific degradation of the photoluminescence properties of GaInAsN quantum wells (QW), and consequently of the lasing threshold of GaInAsN-based lasers, occurs due to the N incorporation. In this paper, we have investigated in detail the growth parameters of GaInAsN grown by MOVPE using dimethylhydrazine (DMHy) as nitrogen precursor. We have established that optimized growth conditions further away from standard parameters can lead to a strong improvement of both PL and lasing characteristics. Thus, a low-pressure MOVPE process combined with low growth temperature and growth rate, as well as the choice of specific low cracking temperature group-V and III precursors such as DMHy, TBAs and TEGa are essential to achieve GaInAsN material suitable for laser devices. By this way, we have achieved lasing at 1.26 μm with a threshold current density as low as 540A/cm2.

Low bandgap nitrides, such as GaInAsN, grown on GaAs substrates have received a large amount of attention for several years as an alternative material system to the mature GaInAsP/InP semiconductor system, especially for 1.3 μm emission. However, to obtain high-quality GaInAsN material suitable for laser applications, it is required to overcome several specific growth issues, which are reviewed in this paper for the metal organic vapor phase epitaxy (MOVPE) technique as compared to MBE. We have particularly established that the incorporation of nitrogen in Ga(In)As grown by MOVPE requires specific growth conditions, which can result in strong improvement of both photoluminescence and lasing characteristics. The performance of GaAs-based long-wavelength lasers, as well as those from the recent literature, are compared to the state-of-the-art InP-based lasers.

We have studied photoluminescence (PL) properties of GaInNAs quantum wells (QWs) which have GaInAs intermediate layers (IML) inserted at the GaInNAs/GaAs heterointerfaces. Lasing characteristics of the laser using IML are also investigated. We point out that the total amount of nitrogen (N) in the GaInNAs QW could be reduced by using the GaInAs IML while maintaining the emission wavelength. We also found that the optical quality of the GaInNAs IML QWs depends on both the N composition and the total amount of N incorporated in the QW. Due to the reduced total amount of N, an IML QW evidently exhibited a better PL property than a conventional rectangular potential QW. No deterioration in lasing characteristics was observed for GaInNAs lasers using GaInAs IML. The GaInAs IML structure with an appropriate design is expected to lead to improved lasing characteristics of GaInNAs lasers.

We investigate the effect of the sequence of gas flows at heterointerfaces on optical quality of GaInNAs/GaAs quantum wells grown by metalorganic chemical vapor deposition (MOCVD). We point out that the degradation mechanism of photoluminescence of GaInNAs grown by MOCVD method is categorized in two types. One is the formation of a GaNAs layer at the heterointerface which causes both increase of emission wavelength and degradation of crystal quality. The other is generation of nonradiative centers induced by incorporation of nitrogen (N). The insertion of a GaInAs layer to the GaInNAs/GaAs heterointerface is proposed to overcome these degradation mechanisms. A GaInAs intermediate layer is effective to suppress the GaNAs formation and to reduce the total GaInNAs thickness.

Low bandgap nitrides such as GaInAsN grown on GaAs substrate have received a large amount of interest for several years as an alternative material system to the Well matured GaInAsP/InP semiconductor system especially for 1.3 mum emission. However, to reach high quality GalnAsN material suitable for laser applications, it is required to overcome several specific growth issues, which are reviewed in this paper for MOVPE technique as compared to MBE. We have particularly established that the incorporation of nitrogen in Ga(In)As grown by MOVPE requires specific growth conditions, which can result in strong improvement of both photoluminescence and lasing characteristics. Our performances of GaAs-based long wavelength lasers as well as those from the recent literature are compared to the state of art of InP-based lasers.

We have achieved the lowest threshold current density of 340 A/cm/sup 2/ with a high characteristic temperature of over 200 K in 1.25 /spl mu/m GaInNAs/GaAs lasers grown by MOCVD. A threshold current density per well of 170 A/cm/sup 2/ is the record low value for 1.2/spl sim/1.3 /spl mu/m GaInNAs lasers.

In this study, we demonstrate a highly strained 1.2 µm GaInAs/GaAs quantum well laser which may be used in high-speed local area networks. Edge emitting lasers with either a GaInP or AlGaAs cladding layer have been fabricated. We have achieved a threshold current density as low as 170 A/cm2 for GaInP-cladding-layer lasers and a high characteristic temperature T 0 as high as 211 K from 30°C to 120°C for AlGaAs-cladding-layer lasers. The material gain coefficient g 0 was estimated to be 1550 cm-1 which is comparable to that of 0.98 µm GaInAs lasers. A preliminary lifetime test under heatsink-free CW condition was carried out, which shows no notable degradation after 300 h. We also demonstrated an AlAs oxide confinement laser in a 1.2 µm wavelength band.

We investigated the effect of the gas flow sequence of dimethylhydrazine (DMHy) at hetero interfaces on the optical quality of GaInNAs/GaAs grown by metalorganic chemical vapor deposition (MOCVD). We point out that the photoluminescence (PL) degradation of GaInNAs grown by MOCVD can be categorized into two types. One is the formation of a GaNAs layer at the interface which causes both an unexpected wavelength extension and degradation of crystal quality. Another is introduction of non-radiative centers by N incorporation itself. To overcome these degradation mechanisms, the insertion of GaInAs to the GaInNAs/GaAs heterointerface is proposed. A GaInAs intermediate layer (IML) suppresses GaNAs formation and improve the optical quality of GaInNAs QWs.

We report on the lasing characteristics of low-threshold long-wavelength GaInNAs double quantum well (DQW) lasers grown by metalorganic chemical vapor deposition (MOCVD). We have achieved a threshold current density of 450 A/cm2 for a 1.28-µm-emitting laser. This is the lowest value for 1.3-µm-range GaInNAs lasers grown by MOCVD. We also observed high characteristic temperatures (T 0) of 210 K and 130 K for 1.25 µm and 1.28 µm lasers, respectively. In addition, we investigated the gradual change in lasing characteristics under pulsed operation. The blue shift of an emission wavelength and a threshold current reduction were observed, which is similar to that observed in the thermal annealing of GaInNAs.

In this paper we experimentally determined the critical layer thickness for highly strained 1.2-μm GaInAs/GaAs quantum wells of good crystal quality. The dependence of the critical layer thickness on the indium content indicates that the observed quality degradation is caused by a growth mode transition. This is also supported by transmission electron microscopy measurements. We discuss the possibility of extending the wavelength of highly strained GaInAs/GaAs quantum wells toward 1.3μm by delaying the growth mode transition. As a first step, a wavelength extension to 1.225μm is achieved by using the presented technique.

GaInNAs/GaAs quantum wells with indium compositions of up to 39% were grown by metalorganic chemical vapor deposition under different growth rates. We found that the growth rate (∼1 µm/h) critically affects the optical quality of GaInNAs/GaAs quantum wells and that a low growth rate (∼0.2 µm/h) is preferable for increasing nitrogen compositions.

A new and simple treatment of miscibility gap calculations for ternary and quaternary semiconductors including strain is presented. Our treatment leads to the same result as that of previous treatments: in the case of lattice-matched layers, but provides a more realistic and rigorous description for coherently strained layers. We also discuss the differences between our treatment and previous treatments, including misfit strain caused by the substrate. Our treatment is applied in miscibility gap calculations for GaInNAs and GaInAsSb material systems. Theoretical predictions by miscibility gap calculations are compared with growth experiments and show reasonable agreement.

A metal organic chemical vapour deposition grown GaInNAs quantum well laser emitting at 1.25 mum is reported. The lowest threshold current density obtained by 50 mum wide stripe lasers was 340A/cm(2) for a cavity length of 1420 mum, which is almost comparable to the lowest value reported for GaInNAs lasers grown by molecular beam epitaxy. The threshold current density per well was 170A/cm(2), which is the lowest threshold value reported to date.

We investigated the crystal quality dependence of GaInNAs/GaAs quantum wells (QWs) on the growth rate for metalorganic chemical vapor deposition (MOCVD). GaInNAs QWs were grown under different growth rates of 0.15, 0.2, 0.6 and 1 /spl mu/m/h. At a growth rate of 0.2 /spl mu/m/h, GaInNAs QWs showed the smallest degradation on photoluminescence (PL) for elongating the wavelength by increasing nitrogen (N) composition. GaInNAs QW stripe lasers, which employ a GaInNAs double QWs (DQWs) active layer grown at the optimized growth rate, exhibits a threshold current density of 340 A/cm/sup 2/, which is the lowest for MOCVD grown GaInNAs lasers ever reported.