An Investigation of Semiconductor Quantum Well Structures With Modulatıon Spectroscopy
In this study, electrooptic properties of bulk semiconductor and low dimensional heterostructures were investigated by photoreflection method at room temperature. Photoreflection is one of the modulation spectroscopy methods. Because of derivative nature of modulation spectroscopy, the changes can easily be observed with this technique.
In this study, bulk GaAs was chosen as a test sample and then as low dimensional structures HELLISH VCSEL and UB HELLISH samples were investigated.
The aim of using the bulk GaAs was to test the experimental set-up. The band gap of semiinsulator GaAs which was measured by photoreflection method as 1.42 eV at room temperature. This value is consistent with the literature.
At HELLISH VCSEL (Hot Electron Light Emitting and Lasing in Semiconductor Heterostructure Vertical Cavity Surface Emitting Laser) samples, the active region is sandwiched between Distributed Bragg Reflector (DBR) which is used as reflecting mirrors for vertical cavity lasers and the wavelength which is a dip value of the reflectivity spectrum, which is the cavity resonance value. This wavelength which depends on the growth parameters is determined at 830nm by using finite quantum well approximation. It is found that the measured cavity resonance wavelength depends on the position of sample where the reflection measurements taken. It is believed that the reason of this change is probably due to the growth technique of DBR layers
Althought, the other sample used in this work is different then the HELLISH VCSEL samples they also shows similar behavior for the reflection spectrum. Since, only difference is that the top DBR layers are removed in this sample, its emission intensity is very high (therefore, it is called as Ultra Bright HELLISH ). The effective band gap of the active region of UB HELLISH was determined to be consistent with the results of reflection.