Jiangang Ma

Influence of oxygen passivation on optical properties of PbSe thin films

A series of PbSe thin films grown on a (111)-oriented Si substrate by molecular beam epitaxy were passivated by high-purity oxygen at different annealing temperatures. The photoluminescence intensity increased by more than two orders of magnitude at 4.5μm after annealing the samples in an O2 atmosphere at 350°C. X-ray photoelectron spectroscopy revealed that PbO and SeO2 were formed during the oxidation process of PbSe, thus confirming the formation of the surface passivation layer which resulted in the observed significant increase in PL intensity.

Room temperature mid-infrared surface-emitting photonic crystal laser on silicon

We demonstrate a mid-infrared surface-emitting photonic crystal laser on silicon substrate operating at room temperature. The active region consisting of PbSe/PbSrSe multiple quantum wells was grown by molecular beam epitaxy on Si(111) substrate patterned with a photonic crystal (PC) array. The PC array forms a transverse magnetic polarized photonic bandgap at around 2840 cm−1. Under pulsed optical pumping, room temperature multimode lasing emissions were observed at wavelength ∼3.5 μm with estimated threshold peak pumping intensity of 24 kW/cm2. Angular-dependent measurement indicates the lasing is of a Gaussian-like profile with full width at half maximum of 4.66°.

Elimination of threading dislocations in as-grown PbSe film on patterned Si(111) substrate using molecular beam epitaxy

A high-quality as-grown PbSe film with a record low threading dislocation density of 9×105 cm−2 on patterned Si(111) substrate has been obtained using molecular beam epitaxy. The mechanisms leading to the remarkable reduction in threading dislocation density are analyzed. Based on the analysis, further reduction in dislocation density is anticipated. Materials with such low dislocation density should significantly improve the Si-based IV-VI group device performance.

Growth mechanism of cuboid growth pits in lead selenide epilayers grown by molecular beam epitaxy

Microstructures and crystallographic orientations of cuboid growth pits in lead selenide (PbSe) epilayers grown on Si (1 1 1) by molecular beam epitaxy (MBE) have been studied by scanning electron microscopy and cross-sectional transmission electron microscopy. Cuboid density was found to be dependent on MBE growth parameters such as sample thickness and substrate temperature. Cuboid growth defects nucleate spontaneously on the PbSe growth surface probably at Pb droplets. This nucleation results in randomly oriented PbSe crystallites that preferentially grow along the [1 0 0] axis of the NaCl-type crystal structure. This preferential growth results in cuboid crystallites with cubic faces protruding from the epitaxial (1 1 1) face.

Mid-infrared surface-emitting photonic crystal microcavity light emitter on silicon

We describe an IV-VI semiconductor light emitter consisting of a PbSe/PbSrSe multiple quantum well active region grown by molecular beam epitaxy on a patterned Si(111) substrate with a two dimensional (2D) photonic crystal (PC) array. The 2D PC array was designed to form photonic band gaps around 1960 and 2300 cm−1. Under pulsed optical pumping, light emission was observed with strongly coupled PC defect modes, which correspond well with simulated photonic band gaps. The observed spectral linewidth was around 10 cm−1 and the highest quantum efficiency measured was 12.8%.

Modeling of the Potential Profile for the Annealed Polycrystalline PbSe Film

A new model for the mechanism of photoconductivity in annealed polycrystalline PbSe fllm is presented. The combined mechanism with respect to double heterojunction due to oxidation layer, dopant segregation and carrier trapping at grain-boundary is proposed. This letter focuses on characterizing the potential proflle, which is extremely important from the viewpoint of carrier transport phenomena. A potential proflle adjacent to the boundaries was calculated, and the efiect of biased voltage was in detail discussed, which shows that the mech- anism of photoconductivity of annealed polycrystalline PbSe fllm depends on properties of the grain boundaries.