Abstract In this thesis, we have setup a photoluminescence (PL) measurement system to investigate the quantum well intermixing (QWI) effects on semiconductor multiple quantum-well (MQW) structures. The measured samples include 1.3mm and 1.55mm InGaAsP MQW laser structures grown by MOCVD, and 1.55mm InGaAlAs MQW structures by MBE. The QWI process was performed by rapid thermal annealing at 600¢J~800¢J in 1 min with a ~1300Å SiO2 layer sputtered on the semiconductor surface. Following the SiO2 sputtering and thermal annealing, room-temperature PL measurements were used to study the QWI effect. The result shows that the PL intensity is reduced for the MOCVD samples, while the MBE samples have up to 47 times increase of PL intensity. After QWI process, all the samples have a blue-shift in PL spectra. The 1.55mm InGaAsP laser structures by MOCVD have a maximum blue-shift of 34nm, and the MBE samples of 12nm after 800¢J annealing.

The two-dimensional electron system in strongly coupled GaAs/Al0.3Ga0.7As double quantum wells has been studied by Shubnikov-de Haas¡]SdH¡^measurements. The degenerate subbands of the double quantum wells are lift into two subbands with a symmetric or anti- symmetric z-direction wave function. We observed that the SdH oscillation due to the second subband of anti-symmetric wave function. The effective mass of the second subband is linearly dependent on the magnetic field range from 0.680 T to 1.964 T. The mass enhancement for the double-quantum-well with an equal well thickness is greater than that with an unequal one. This mass enhancement is attributed to the electron-electron interaction.

From PL spectrum of InGaAsN LD structures grown by MOCVD and MBE, we observe remarkable red shift of the wavelength after the addition of small concentration of nitrogen. For MOCVD growth, the concentration of nitrogen increases from 0.3% to 0.5%, and the wavelength improve from 1.17£gm to 1.202£gm. For MBE growth, the concentration of nitrogen increases from 2.1% to 2.6%, and the wavelength improve from 1.196£gm to 1.289£gm. When the concentration arrived 3%, we find the wavelength already unable to improve to long wavelength. We also observed the changes the PL peak like S-shaped from temperature-depentent PL spectrum. For the photocurrent and electroabsorption measurement, we prepared two the same concentration of nitrogen 2.1% samples, but different structures ,one is TR538 single quantum well structure, the other is TR515 double quantum well structure. The e1-hh1transition can be observed clear at £f=1.192 of TR515, but it was unapparent for TR538. Now, let us focus on the photocurrent and £G£\ signal of the fundamental e1-hh1 transitions for the largest reverse bias voltage swing(0-6v) , the maximum absorption changes of around 5394cm-1 for TR538 and 14439cm-1 for TR515. The refractive index changes of 0.019 for TR538 and 0.035 for TR515.

In this work, a quantum well intermixing(QWI) technology, called impurity free vacancy diffusion(IFVD), is used to do the bandgap engineering in an optoelectronic monolithic integration. The monolithic integration of SOAs and EAMs is taken as an example. By IFVD, the transition energy levels of EAM quantum wells can be shifted to shorter wavelength regime, while SOA quantum wells are kept the same. Therefore, the overall SOA-integrated EAM efficiency can be improved. A 400nm thick SiO2 is sputtered at the EAM regions to locally create defects in the surface of pin InGaAsP/Imp layer structure. Rapid thermal Annealing (RTA) technique at 850oC is then used to inter-diffuse the atom of quantum wells. A SOA-integrated EAM is fabricated on such template. Ti/Pt/Au and Ni/AuGe/Ni/Au are used for p-type and n-type metallization. An optical waveguide structure is defined by selective undercut-etching active region. The PMGI is spun for planarization and bridging. A Ti/Au is finally deposited as microwave coplanar waveguide. A DC measurement of photocurrent spectrum is performed to examine the wavelength shift. A 10nm shift is found between EAM and SOA regions. Modulation efficiency of 15dB/V with extinction ratio of higher than 20dB is observed in EAM device. And the optical gain of SOA is found as 3dB at 1540nm excitation wavelength. -3dB bandwidth of 20GHz is obtained. In comparison with sample without intermixing, the same results are achieved in intermixing sample, suggesting no regrowth processing is needed for obtaining the same quality of optoelectronic integration.

Group III nitrides are efficient light emitters. The modification of internal optoelectronic properties of these materials due to strain, external or internal electric field are an area of interest. Insertion of metal nanoparticles (MNPs) (Ag, Au etc) inside the V-shaped inverted hexagonal pits (IHP) of InGaN/GaN quantum wells (QWs) offers the potential of improving the light emission efficiencies. We have observed redshift and blueshift due to the Au MNPs and Ag MNPs respectively. This shift could be due to the electric field created by the MNPs through electrostatic image charge. We have studied the ultrafast carrier dynamics of carriers in hybrid InGaN/GaN QWs. The change in quantum confinement stark effect due to MNPs plays an important role for slow and fast carrier dynamics. We have also observed the image charge effect on the ultrafast differential transmission measurement due to the MNPs. We have studied the non-linear absorption spectroscopy of these materials. The QWs behave as a discharging of a nanocapacitor for the screening of the piezoelectric field due to the photo-excited carriers. We have separated out screening and excitonic bleaching components from the main differential absorption spectra of InGaN/GaN QWs.

No description available.

No description available.

Resonant or near resonant optical nonlinearities in semiconductor coupled quantum-well systems are discussed. Quantum engineered coupled or cascade quantumwell structures can provide giant nonlinear susceptibilities for various optical nonlinear processes. Nonlinearities integrated within quantum cascade lasers (QCL) showed great potential in various applications in the infrared range. Several schemes of nonlinearities are proposed and discussed in this work. Integrating difference frequency generation (DFG) with QCL can yield long wavelength radiation, such as terahertz light. The DFG process does not require population inversion at a transition associated with low photon energy; however, this requirement is necessary to lasers, such as QCL, and is hard to meet, because of the thermal backfilling and inefficient injection or pumping at room temperature. Therefore terahertz radiation due to DFG QCL for room temperature is proposed. On the other hand, the second harmonic generation can double laser frequency, and then push radiation frequency of AlInAs/GaInAs/InP based QCL to short wavelengths such as 3 μm and shorter. Optical nonlinearities can extend working frequencies of light sources, and also can help to improve light detection. For example, a sum frequency generation can upconvert mid/far-IR signal into near-IR signal with strong near-IR pump light, namely high efficient near-IR photon detector could be employed to detect mid/far-IR light. A specific designed quantum well structure of this frequency up-conversion scheme is discussed. A scheme of monolithic in-plane integration of the optical nonlinearities with QCL is also proposed. In this scheme, an optical nonlinear section is made from the same quantum well structure of a QCL, and is under an independent applied bias. Due to the independence of the applied bias, the nonlinearities can be tuned flexibly. In particular, a widely tunable Raman laser based on this scheme could be achieved. A frequency up-conversion based on sum frequency generation process in coupled quantum-well structure is also proposed for mid-infrared detection. By converting mid-IR signal to near-IR, superior near-IR detector such as silicon avalanche photo diode (APD) can be employed. The scheme can provide lower noise equivalent power (NEP) or higher detectivity compared with regular semiconductor photo detectors. A scheme of lasing without inversion (LWI) based on QCL for THz radiation is proposed. A ladder type three-level system for LWI process is integrated into a boundto- continue high power QCL at 10 μm. The proposed LWI generates THz signal at 69 μm. An optical gain about 80 cm-1 is achieved, against a waveguide loss about 30 cm-1 in a semi insulator (SI) surface plasmon waveguide.

We intend to study the magneto-transport properties of two dimensional electron-hole systems in the condition of ultra-low temperature and high magnetic field by SdH measurement and QHE measurement. In these samples, the SdH oscillations show a 2DEG behavior. We observed that the sample shows negative persistent photoconductivity effect at low temperature and high field under illumination. We want to compare with results before 4 years, so we change more sets of measurement. And we want to know if these samples still show the same effect after 4 years.

No description available.