The need to monitor growth of structures increase as the structure of applications gets more complicated. Nowadays the active region of several components are often one or more quantum wells (QWs). However, typically only in-situ monitoring of thick layers is considered to be possible. QW monitoring is enabled when the wavelength of the light used for in-situ monitoring is absorbed into the material under monitoring. When dilute nitride QW growth is monitored also answers to some material research and growth related issues are revealed. In addition, the complex refractive indices of several materials with several compositions are obtained in high temperature (the growth temperature is typically between 500 and 600 degrees C) at wavelength 635 nm. FIG. 2. shows in-situ reflectance curve measured during growth of InGaAsN/GaAs multi-QW structure and below that a theoretical curve is shown. The theoretical curve has been obtained using matrix method. The real and imaginary parts of the material complex refractive index are obtained by simulations. The real and imaginary parts of the complex refractive index of InGaAs are shown in FIG. 3. Both exhibit a clear trend with increasing indium content. Because of the clear trend observed, the real time analysis of the QWs is made possible. Typically the composition analysis of quarternary alloys is fairly difficult (for example by XRD measurements). However, complex refractive index measured during growth provides both real and imaginary parts for the composition analysis. Luckily it turns out that the real parts of complex refractive indices of nitrogen containing GaAs based materials are independent of the nitrogen content. Furthermore, the imaginary parts are strongly nitrogen dependent as shown in FIG. 4. The knowledge of the complex refractive indices of different materials at their growth temperature enables the analysis of the compositions of the materials already during growth. Additionally, the material quality can be roughly assessed during growth.
No hay comentarios:
Publicar un comentario