G. Baldassarri Höger von Högersthal

Early manifestation of localization effects in diluted Ga(AsN)

The electron effective mass, me, and extent of exciton wave function, rexc, were derived in GaAs1-yNy (y=0.043%–0.5%) from magnetophotoluminescence measurements. With an increase in nitrogen concentration, we find that me and rexc undergo a rapid increase and squeezing, respectively, even for y≈0.1%. This quite early manifestation of nitrogen-induced localization effects imposes important constraints on existing theoretical models.

Role of hydrogen in III–N–V compound semiconductors

The role of hydrogen in altering the electronic properties of the InxGa1?xAs1?yNy/GaAs system has been investigated by photoluminescence (PL) spectroscopy. Several heterostructures whose nitrogen concentration, y, spans from the dilute (0.0001 ? y ? 0.001) to the alloy (0.01 ? y ? 0.052) limit have been studied. The most remarkable effects observed are a quenching of the PL lines related to exciton recombination in N complexes in the dilute limit, and a bandgap blueshift of the N-containing material towards that of the N-free reference samples in the alloy limit. Differences and similarities found between In-free and x = 0.25?0.41 samples are highlighted. In all cases, the system fully recovers by thermal annealing the optical properties it had before hydrogenation. These behaviours can be accounted for by the formation of N?H bonds, which leads to an effective electronic passivation of the N atoms in the lattice. An analysis of the annealing experiments provides some clues on the geometry of the N complexes in the dilute limit as well as an estimate of the N?H bond strength in both dilute and alloy limits. All these results show that the charge distribution around the N atoms maintains in the alloy limit the strongly localized character it has in the impurity limit.

High temperature photoluminescence efficiency and thermal stability of (InGa)(AsN)/GaAs quantum wells

The temperature dependence of the photoluminescence (PL) efficiency of (InGa)(AsN)/GaAs single quantum wells (QWs) has been studied from 10 to 500 K. The PL intensity of N-containing samples is almost constant from room temperature to 500 K, in contrast to what is observed in (InGa)As QWs grown under the same conditions. This thermal stability increases for an increase in nitrogen content. We discuss these effects in terms of strain compensation at high nitrogen concentrations.

Single carrier localization in InxGa1-xAs1-yNy investigated by magnetophotoluminescence

We investigated the origin of radiative recombination in InxGa1−xAs1−yNy/GaAs quantum wells by photoluminescence (PL) after picosecond excitation and under a magnetic field, B. Continuous wave and time-resolved PL show that at low temperature T localized states are mainly involved in the radiative recombination processes. Most importantly, the shift of the PL peak position induced by B depends dramatically on temperature, being higher at lower T. This result indicates that the PL emission at low temperature is determined by the recombination of loosely bound electron-hole pairs in which one carrier is localized by N-induced potential fluctuations, and the other carrier is delocalized.

Hydrogen as a probe of the electronic properties of (InGa)(AsN)/GaAs heterostructures

We report on the effects of N incorporation on the electronic properties of (InGa)(AsN)/GaAs heterostructures as investigated by photoluminescence (PL) spectroscopy. PL under a magnetic field shows an increase in the electron effective mass in the N-containing material. In order to address this effect as well as the giant band gap reduction induced by N in (InGa)As, we exploit the ability of hydrogen to passivate the electronic activity of N in (InGa)(AsN). Such passivation is due to the formation of N–H bonds and manifests itself as: (i) a quenching of the exciton recombination in N-related complexes in the N dilute limit; (ii) a blueshift of the (InGa)(AsN) band gap toward that of the N-free material in the alloy limit. A thermal annealing leads to a complete recovery of the electronic properties (InGa)(AsN) had before H irradiation in both limits.The activation energy for the thermal dissociation, ED, of the N–H complexes follows a Gaussian distribution with a mean value increasing with the N concentration, y. Values of ED similar to those found in the alloy limit are found in the case of very dilute N concentrations (impurity limit), where different N–H complexes are singled out. These results show that different N complexes are responsible for the puzzling effects exerted by N on the electronic properties of (InGa)(AsN).

Magnetophotoluminescence studies of InxGa1-xAs1-yNy: a measurement of the electron effective mass, exciton size, and degree of carrier localization

Photoluminescence (PL) under a magnetic field (B = 0–12 T) has been employed to determine the electron effective mass, me*, exciton radius, rexc, and degree of localization of carriers in InxGa1−xAs1−yNy/GaAs heterostructures. This study concerns nitrogen concentration values spanning from a very dilute (y<0.1%) to a full alloy (y = 5%) limit and indium concentrations x from 0% to . For indium-free samples, we find that me* and rexc undergo a sudden increase and squeezing, respectively, for . For indium-containing samples (), me* and rexc show a sudden variation similar to that for x = 0 but shifted to much higher N concentration (). In addition, in the N alloy limit the temperature dependence of the B-induced shift of the PL peak position reveals that radiative recombination at low temperature is not excitonic.

Measurement of Carrier Localization Degree, Electron Effective Mass, and Excition Size in In x Ga 1−x As 1−y N y Alloys

We employ photoluminescence under a magnetic field to investigate the electronic properties of In x Ga 1-x As 1-y N y /GaAs heterostructures. We studied samples with nitrogen concentration from the doping (y y = 2.0%. In particular, by exploiting the capability of post-growth hydrogen irradiation to tune finely the electronic properties of GaAs1-yNy, we are able to assess that a major change in me and in rexc takes place within a very narrow interval of N concentrations, which is centred at y = 0.1%. Alloying of GaAs1-yNy with In (x ~ 0.3) results in a shift of such interval to y = 1.0%.

Nitrogen-Related Complexes in Ga(AsN) and Their Interaction with Hydrogen

The effects of H irradiation on the optical properties of GaAs 1-y N y epilayers in the dilute N limit have been studied. H irradiation leads to a progressive and finally complete passivation of bound exciton levels related to N complexes. A further thermal annealing restores the optical properties that the samples had before hydrogenation. These results are accounted for by the formation of N-H complexes with different bond strengths and dissociation energies.

Reversibility of the effects of hydrogen on the electronic properties of InxGa1-xAs1-yNy

Abstract The effects of post-growth hydrogen irradiation and subsequent thermal annealing on the electronic properties of (InGa)(AsN) single quantum wells (QWs) have been studied by photoluminescence spectroscopy. We find that the QW effective band gap increases as a result of hydrogen irradiation and may reach the value it has in a N-free reference sample. Thermal annealing, instead, restores the optical properties the QW had before hydrogenation. These results are accounted for by the formation of N–H complexes, with an ensuing N passivation and a reduction of the effective N concentration. By means of isochronal annealings performed at different temperatures we determine the activation energy for the dissociation of such complexes, which has a Gaussian distribution. We attribute this finding to N clusters with different size forming different H–N bonds.