P. Laukkanen

Low-threshold-current 1.32-μm GaInNAs/GaAs single-quantum-well lasers grown by molecular-beam epitaxy

Using solid-source molecular-beam epitaxy with a rf-plasma source, we have grown GaInNAs/GaAs single-quantum-well lasers operating at 1.32 μm. For a broad-area oxide stripe, uncoated Fabry–Perot laser with a cavity length of 1600 μm, the threshold current density is 546u200aA/cm2 at room temperature. The internal quantum efficiency for these lasers is 80%, while the materials losses are 7.0u200acm−1. A characteristic temperature of 104 K was measured in the temperature range from 20 to 80u200a°C. Optical output up to 40 mW per facet under continuous-wave operation was achieved for these uncoated lasers at room temperature.

Postgrowth annealing of GaInAs∕GaAs and GaInAsN∕GaAs quantum well samples placed in a proximity GaAs box: A simple method to improve the crystalline quality

The effects of thermal annealing on GaInAs∕GaAs and GaInAsN∕GaAs quantum wells, grown by molecular beam epitaxy, were investigated. Optical and structural properties were examined upon annealing when the samples had a 200nm thick SiO2 cap layer, or were placed in a so-called GaAs box or were left uncapped. The GaAs box gave rise to the strongest photoluminescence without significant blueshift or structural changes at moderate annealing temperature. Capping with SiO2 impaired the samples and caused a more pronounced blueshift for the GaInAs quantum wells than for the GaInAsN ones. These results consolidate our understanding of the blueshift mechanisms.

Enhanced optical performances of strain-compensated 1.3-μm GaInNAs/GaNAs/GaAs quantum-well structures

We report on luminescence properties of GaInNAs/GaNAs/GaAs quantum-well structures emitting light at the wavelength of 1.3 μm, grown by molecular beam epitaxy. The design of the structure consists of a strain-mediating GaInNAs layer, sandwiched between a highly compressive GaInNAs quantum well and a strain-compensating GaNAs layer. Insertion of the strain-mediating layer improves optical activity of the quantum well and shifts the spectrum to longer wavelengths.

Effects of (NH4)2S and NH4OH surface treatments prior to SiO2 capping and thermal annealing on 1.3 μm GaInAsN/GaAs quantum well structures

We report the influence of (NH4)2S and NH4OH surface treatments prior to SiO2 capping and subsequent rapid thermal annealing, on optical properties of GaInAsN/GaAs quantum-well (QW) structures. We observed an increase in QW photoluminescence (PL) emission for the (NH4)2S treated samples as compared to the untreated sample. After annealing, also the NH4OH treated sample showed significant improvement in PL. The treatments were also found to decrease the In out-diffusion and reduce the blueshift upon annealing. The PL results are discussed with x-ray diffraction and x-ray photoemission data from SiO2/GaAs, in particular, with changes found in Gau20023d spectra.

Emission studies of InGaN layers and LEDs grown by plasma-assisted MBE

Abstract We prepared InGaN layers on GaN/sapphire substrates using rf-MBE. Photoluminescence (PL) from these layers, grown at different temperatures T S , shows that there is a strong tendency of GaN to form a separate phase as T S is increased from 600°C to 650°C. Concomitant with the phase separation, the PL from the InGaN phase broadens, which indicates that indium composition in this phase becomes increasingly non-uniform. Indium compositions measured by Rutherford backscattering (RBS) are consistent with these results. We also observed an increase in PL intensity for InGaN layers grown at higher temperatures. In this paper, we also report on preparing a top-contact InGaN/GaN light emitting diode. The device was operated at 447xa0nm and had the emission line width of 37xa0nm with no observable impurity related features. The turn-on voltage was 3.0xa0V. The output power was 20xa0μW at 60xa0mA drive current.

Properties of the SiO2- and SiNx-capped GaAs(100) surfaces of GaInAsN/GaAs quantum-well heterostructures studied by photoelectron spectroscopy and photoluminescence

SiO2 and SiNx layers are routinely deposited onto III-V(100) surfaces at different device processing steps. We elucidate these insulator-interface properties with photoemission and photoluminescence (PL) of SiO2- and SiNx-capped GaAs(100) surfaces of GaInAsN/GaAs quantum wells (QWs). Post-growth annealing led to an increase of the QW-PL intensity, of which origin can be clearly linked to the SiO2 and SiNx interfaces. Concomitantly, Ga2O–related photoemission increased, indicating useful formation of Ga2O at both insulator interfaces. Furthermore, higher Ga-oxidation-state emission, identified with Ga diffused into SiO2 and SiNx, correlates with the blue-shift of the QW-PL wavelength. Also, interfacial As-As related photoemission was identified.

The influence of As/III pressure ratio on nitrogen nearest-neighbor environments in as-grown GaInNAs quantum wells

The energy fine structure, corresponding to different nitrogen nearest-neighbor environments, was observed in contactless electroreflectance (CER) spectra of as-grown GaInNAs quantum wells (QWs) obtained at various As/III pressure ratios. In the spectral range of the fundamental transition, two CER resonances were detected for samples grown at low As pressures whereas only one CER resonance was observed for samples obtained at higher As pressures. This resonance corresponds to the most favorable nitrogen nearest-neighbor environment in terms of the total crystal energy. It means that the nitrogen nearest-neighbor environment in GaInNAs QWs can be controlled in molecular beam epitaxy process by As/III pressure ratio.

Growth and properties of crystalline barium oxide on the GaAs(100) substrate

Growing a crystalline oxide film on III-V semiconductor renders possible approaches to improve operation of electronics and optoelectronics heterostructures such as oxide/semiconductor junctions for transistors and window layers for solar cells. We demonstrate the growth of crystalline barium oxide (BaO) on GaAs(100) at low temperatures, even down to room temperature. Photoluminescence (PL) measurements reveal that the amount of interface defects is reduced for BaO/GaAs, compared to Al2O3/GaAs, suggesting that BaO is a useful buffer layer to passivate the surface of the III-V device material. PL and photoemission data show that the produced junction tolerates the post heating around 600u2009°C.

Ultrathin (1x2)-Sn layer on GaAs(100) and InAs(100) substrates: A catalyst for removal of amorphous surface oxides

Amorphous surface oxides of III-V semiconductors are harmful in many contexts of device development. Using low-energy electron diffraction and photoelectron spectroscopy, we demonstrate that surface oxides formed at Sn-capped GaAs(100) and InAs(100) surfaces in air are effectively removed by heating. This Sn-mediated oxide desorption procedure results in the initial well-defined Sn-stabilized (1x2) surface even for samples exposed to air for a prolonged time. Based on ab initio calculations we propose that the phenomenon is due to indirect and direct effects of Sn. The Sn-induced surface composition weakens oxygen adsorption.

Contactless electroreflectance study of band bending in Be-doped GaInNAs/GaAs quantum wells: The origin of photoluminescence enhancement

Contactless electroreflectance (CER) has been applied to study band bending in Be-doped GaInNAs/GaAs quantum wells (QWs). It has been shown that (i) the sign of GaAs-related CER signal changes from positive to negative due to Be-doping and (ii) QW-related CER resonances disappear for Be-doped QWs whereas they are clearly observed for un-doped QWs. The two observations indicate a Be-related shift in the Fermi level above the hole levels in the QW region, i.e., the change in band bending in this system. The results point out that the experimentally-observed enhancement in QW photoluminescence upon Be-doping is associated with a better collection/confinement of photogenerated carriers by the Be-doped GaInNAs QW.