SiN Capping Layer Research Articles

Dielectric cap disordering of GaAs/AIGaAs multiple quantum well by using plasma enhanced chemical vapour deposited SiN capping layer

The multiple quantum well (MQW) structure is a good candidate for the monolithic integration of lasers and waveguides to realize photonic integrated circuits (PIC). For such an application, certain types of technique are needed to define different bandgaps at the active and passive part of the PIC. Quantum well disordering techniques [1-9] have been used to locally disorder the MQW structure without any regrowth and/or selective growth step. Since the disordering of MQW results in a blue shift in bandgap and an increase in refractive index near the bandgap, these techniques can be used to fabricate lasers and waveguides monolithically with only onestep epitaxial growth. There have been several techniques to selectively disorder III-V compound semiconductor QW structures, such as impurity induced disordering [1, 2], ion implantation disordering [3,4], and dielectric cap disordering [5-9]. Among these techniques, since the dielectric cap disordering technique introduces a much lower optical loss compared to the impurity induced disordering and ion implantation techniques which give high optical losses due to high number of defects and high doping concentrations introduced during the disordering process, this technlque is thought to be better suited for fabricating high performance optical waveguide devices. Since a SiO2 Capping layer induces a relatively larger blue shift than a SiN capping layer in a GaAs/A1GaAs QW system, SiO2 is generally used to promote disordering while SiN is used as a mask to prevent bandgap shifts in the capped areas of the devices [5], even though SiN has been used to promote disordering in InGaAs/InGaAsP QW systems [6]. In this study, a dielectric cap disordering of GaAs/ A1GaAs MQW structure using a PECVD SiN capping layer is reported. The blue shift increased together with the thickness of the SiN capping layer as reported for a SiO2 capping layer [7], the amount of blue shift being even larger than a SiO 2 capped sample. We use a GaAs/A1GaAs MQW laser structure which is grown by a metal organic chemical vapour deposition (MOCVD) technique on a Si-doped n ÷ GaAs substrate. The vertical structure of the MQW

Enhanced disordering of GaAs/AIGaAs multiple quantum well by rapid thermal annealing using plasma enhanced chemical vapour deposited SiN capping layer grown at high RF power condition

The multiple quantum well (MQW) structure is a good candidate to monolithically integrate lasers and waveguides for realizing photonic integrated circuits. For such an application, selective disordering techniques are required, because these can make it possible to define a waveguide section laterally by inducing local changes in absorption and refractive indices of a MQW structure, which is needed to fabricate waveguide devices including laser. There are several techniques to selectively disorder the I I I -V MQW structures. These are impurity induced disordering [1,2], ion implantation disordering [3, 4], and impurity-free disordering [5-12] followed by thermal treatment. Impurity induced disordering and ion implantation disordering can disorder MQW structure perfectly, but these techniques introduce many defects and high doping concentrations which may deteriorate the performances of waveguide devices because of losses from scatterings by defects and free carrier absorption in the waveguide. Impurity-free techniques employ dielectrics, such as SiO2 or SiN, a capped annealing technique, which employs rapid thermal annealing (RTA) [5-10] or sealed ampoule annealing with an As overpressure [11, 12]. Impurity-free techniques do not disorder MQW structure completely, but disorder it enough to fabricate waveguides and lasers [9-12]. For impurity-free disordering, there are various film growth techniques, such as chemical vapour deposition (CVD) [11], e-beam evaporation [6, 8, 9], sputtering [5], and plasma enhanced chemical vapour deposition (PECVD) [7, 10, 12], which can deposit SiN and/or Si te films on a MQW structure. The behaviour of disordering is affected by the film quality used in the impurity-free disordering technique. Therefore, if an optimum film growth condition can be found by varying process conditions, then selective disordering can be achieved with the same material without surface degradation which should be accompanied in the disordering process without an encapsulation. The characteristics of film deposited by the PECVD technique can be varied by varying process conditions, such as substrate temperature, ratio of reactant gas, and RF power [13]. As a first step to finding a process-dependent impurity-free disordering, we varied the RF power. We carried out impurity-free disordering using a PECVD SiN cap layer with RTA. We found that this technique could disorder the GaAs/A1GaAs MQW structure and the disordering was enhanced by using SiN film grown at high RF power. We used a GaAs/A1GaAs MQW laser structure which was grown by a metal organic chemical vapour deposition (MOCVD) technique on Si-doped n ÷ GaAs substrate. The structure has the following layers from the top of the substrate: 0.5/xm of n (1018 cm -3) GaAs buffer, 1/zm of n (1017 cm -3) A10.4~Ga0.s3As, 0.1/xm of undoped A10.24Ga0.76As, four 7 nm undoped GaAs quantum wells with 10 nm A10.24Ga0.76As barrier, 0.1/xm of undoped A10.24Ga0.76As, 1/zm of p (1017 cm -3) A10.47Ga0.53As, and 0.2/xm of p+ (10 ~8 cm -3) GaAs. In the substrate design, separate confinement design is chosen to enhance the optical confinement in the quantum wells. SiN films were deposited by a PECVD technique for cap layers. We used dilute silane (5% Sill4 in N:) and high purity NH 3 (99.999%) and N2 (99.9999%) as a reactant gas. During plasma deposition, the ratio of partial pressure (PNH3/Psi~,) was kept at 1, total pressure was kept as 120 Pa by adding N2 gas and the substrate temperature was 300 °C. SiN films were grown with various RF powers (0 W, 60 W and 90 W). The thicknesses and refractive indices, for each RF power condition, were determined by an ellipsometer (Gaertner, Ll17) and a surface profiler (Tencor, alpha step 200). Disordering of MQW samples was accomplished by RTA at 850 °C for 35 s in Ar atmosphere with a heating rate of 65 °C/s. Disordering of MQW

High quality GaAs on Si by conformal growth

We propose a simple technique which allows the growth of low defect density GaAs films on Si substrates. This technique is based on conformal vapor phase epitaxy and uses a Si3N4 capping layer, as well as the Si surface itself for growth confinement. The as-grown conformal GaAs films exhibit a spectacular reduction in the density of dislocations, because of the latter blocking either on the Si3N4 cap or on the Si substrate. Dislocation densities below 5×105 cm−2 have been obtained in submicrometer-thick conformal GaAs films.

The Effect of Microstructure and Processing Procedures on the Resistivity of Co-Sputtered W-Si Layers on GaAs Substrates

ABSTRACTThe relationship between microstructure, composition, resistivity and processing procedures of W-Si layers on (100) GaAs was examined for both “as deposited” specimens and specimens annealed at temperatures between 100°C and 1000°C. TEM, EDAX, SIMS, AUGER and four point probe resistivity measurements were employed.The layers, exhibiting a columnar growth structure typical of sputter deposition, are amorphous below ≈ 800°C. At 700°C, the formation of pits, attributed to the outdiffusion of Ga and As into the W-Si layer, is observed at the W-Si/GaAs interface. The Ga and As outdiffusion was confirmed for temperatures above 700°C. The layers annealed between 800°C and 1000°C consist of a polycrystalline mixture of αW, βW and W5Si3 with coarse particles, thought to be W5Si3 precursors, formed along the W-Si/GaAs interface and protruding into the substrate. As the frequency of these protrusions increases with increasing temperature, the resistivity of the W-Si layers decreases.Both the composition and the resistivity of the W-Si thin films are affected by the processing procedure. The Si/W ratio of the W-Si thin films decreases whilst their resistivity significantly increases as a result of etching away the Si3N4 capping layer using HF. It is thought that this is due to the removal of Si-oxides formed within the layer during the W and Si sputtering. The decrease in the Si/W ratio and the increase in resistivity are not observed if an A1N capping layer is used.