Outi Reentilä

Photoluminescence in n and p modulation-doped GaInNAs/GaAs quantum wells

Experimental results concerning the steady-state photoluminescence (PL) studies in n and p modulation doped and undoped GaInNAs/GaAs quantum wells are presented. The effects of modulation, type of doping and nitrogen concentration on the PL and the temperature dependence of the band gap, carrier localization and non-radiative recombination are investigated. Increasing the nitrogen composition decreases energy band gap as expected. The n-type modulation doping eliminates most of the defect-related effects and blue shifts the energy band gap. However, the p-type doping gives rise to additional features in the PL spectra and red shifts energy band gap further compared to the n-type-doped material.

In situ determination of InGaAs and GaAsN composition in multiquantum-well structures

Metal-organic vapor phase epitaxial growth of InGaAs/GaAs and GaAsN/GaAs multiquantum-well (MQW) structures was monitored by in situ reflectometry at 635 nm using a normal incidence reflectance setup. The reflectance signal is found to change significantly during both quantum-well (QW) and barrier growth regions. A matrix method is used to calculate the theoretical reflectance curve and comparing the theoretical curves to the measured ones the complex refractive index of the ternary alloys are derived. Consequently, when the behavior of the complex refractive indices of InGaAs and GaAsN is known as a function of composition, the composition of all the QWs in the MQW strucure can be determined in situ.

In situ determination of nitrogen content in InGaAsN quantum wells

The growth of InGaAsN∕GaAs multiple quantum well structures by metal-organic vapor phase epitaxy is monitored by in situ reflectometry. The nitrogen incorporation is found to depend superlinearly on the precursor flow and a threshold value for the flow is observed. By in situ measurements of the InGaAsN quantum well samples with a fixed indium content, the change in the reflectance during the quantum well growth is found to be linearly dependent on the quantum well nitrogen content. A model to determine the nitrogen content already during the growth is developed. Moreover, the field of application of in situ reflectance monitoring is extended from thick layers to thin layers, including quantum wells.

Temperature Dependence Of Current‐Voltage Characteristics Of Au/p‐GaAsN Schottky Barrier Diodes, With Small N Content

The temperature dependent current‐voltage (IVT) measurements on Au Schottky barrier diodes made on intrinsically p‐type GaAs1−xNx were carried out. Three samples with small N content (x = 0.5%, 0.7% and 1%) were studied. The temperature range was 10–320 K. All contacts were found to be of Schottky type. The ideality factor and the apparent barrier height calculated by using thermionic emission (TE) theory show a strong temperature dependence. The current voltage (IV) curves are fitted based on the TE theory, yielding a zero‐bias carrier height (ΦB0) and a ideality factor (n) that decrease and increase with decreasing temperature, respectively. The linear fitting of ΦB0 vs n and its subsequent evaluation for n = 1 give a zero‐bias ΦB0 in the order of 0.35–0.4 eV. From the reverse‐bias IV study, it is found that the experimental carrier density (NA) values increase with increasing temperature and are in agreement with the intrinsic carrier concentration for GaAs.

Simultaneous determination of indium and nitrogen contents of InGaAsN quantum wells by optical in situ monitoring

In situ monitoring of metal-organic vapor phase epitaxial growth of InGaAsN∕GaAs multiquantum wells is studied. The complex refractive index of InGaAsN is determined for several indium and nitrogen contents based on the fits to the reflectance curve. Taking advantage of the different effects caused by the incorporation of indium and nitrogen on the complex refractive index of InGaAsN, the InGaAsN quantum well nitrogen and indium contents are simultaneously determined in situ.

Comparison of Ge and GaAs substrates for metalorganic vapor phase epitaxy of GaIn(N)As quantum wells

Comparison of Ge and GaAs substrates for the growth of InGaAs and GaInNAs quantum well structures is presented. Quantum well structures are grown simultaneously on both substrates by metalorganic vapor phase epitaxy. Photoluminescence measurements show lower peak energies for the structures grown on Ge than on GaAs. The luminescence redshift between structures grown on Ge and GaAs increases with increasing nitrogen precursor flow. X-ray diffraction analyses indicate that this is due to enhanced N incorporation efficiency on Ge.