Ben Du

Tailoring the performances of low operating voltage InAlAs/InGaAs avalanche photodetectors

We present tailoring of the performances of thin multiplication layer InAlAs/InGaAs avalanche photodetectors (APDs) with operating voltages lower than 20 V. Their operating voltages, gain-voltage slopes and dark currents were successfully tailored by changing the electric field distributions in avalanche region. The thin multiplication layer APDs show small activation energies of the dark current ranging from 0.12 to 0.19 eV at temperatures above 220 K, suggesting a band-trap-band tunneling dominant dark current mechanism over this temperature range. The dark currents show very weak temperature dependences at temperatures lower than 175 K, which mainly originate from the band-to-band tunneling and the surface leakage currents. The spectral responsivity of those APDs show anomalous negative temperature coefficients at gain factors larger than 1, which is attributed to the enhanced phonon scattering effect of carriers in the avalanche region at higher temperatures. Good gain factor uniformity at a given bias is observed for those APDs, and the charge layer is found to help improve the gain uniformity.

Nearly lattice-matched short-wave infrared InGaAsBi detectors on InP

This work reports on the demonstration of a short-wave infrared detector nearly lattice matched to InP substrate using quaternary InGaAsBi as the absorption layer. The bismuth content of about 3.2% has red-shifted the 50% cut-off wavelength from about 1.6 μm to 2.1 μm at room temperature, indicating a bandgap reduction of about 180 meV due to bismuth incorporation. The detector shows an encouraging dark current density of 2.4 × 10−4 A/cm2 at bias voltage of −10 mV at 300 K. This work shows the promising potential of InP-based lattice-matched InGaAsBi detectors for short-wave infrared detection.

InP-based type-I quantum well lasers up to 2.9 μm at 230 K in pulsed mode on a metamorphic buffer

This work reports on up to 2.9 μm lasing at 230 K of InP-based type-I quantum well lasers. This record long wavelength lasing is achieved by applying InP-based Sb-free structures with eight periods of strain-compensated InAs quantum wells grown on metamorphic In0.8Al0.2As template layers. The continuous-wave threshold current density is 797 A/cm2 and the idealized extrapolated threshold current density for infinite cavity length is as low as 58 A/cm2 per quantum well at 120 K. This scheme is a promising pathway for extending the wavelength range of type-I quantum well lasers on InP substrates.

Effect of bismuth surfactant on InP-based highly strained InAs/InGaAs triangular quantum wells

We report the effect of Bi surfactant on the properties of highly strained InAs/InGaAs triangular quantum wells grown on InP substrates. Reduced surface roughness, improved heterostructure interfaces and enhanced photoluminescence intensity at 2.2 μm are observed by moderate Bi-mediated growth. The nonradiative processes are analysed based on temperature-dependent photoluminescence. It is confirmed that Bi incorporation is insignificant in the samples, whereas excessive Bi flux during the growth results in deteriorated performance. The surfactant effect of Bi is promising to improve InP-based highly strained structures while the excess of Bi flux needs to be avoided.

Behaviors of beryllium compensation doping in InGaAsP grown by gas source molecular beam epitaxy

We report structural properties as well as electrical and optical behaviors of beryllium (Be)-doped InGaAsP lattice-matched to InP grown by gas source molecular beam epitaxy. P type layers present a high degree of compensation on the order of 1018 cm−3, and for Be densities below 9.5×1017 cm−3, they are found to be n type. Enhanced incorporation of oxygen during Be doping is observed by secondary ion mass spectroscopy. Be in forms of interstitial donors or donor-like Be-O complexes for cell temperatures below 800°C is proposed to account for such anomalous compensation behaviors. A constant photoluminescence energy of 0.98 eV without any Moss-Burstein shift for Be doping levels up to 1018 cm−3 along with increased emission intensity due to passivation effect of Be is also observed. An increasing number of minority carriers tend to relax via Be defect state-related Shockley-Read-Hall recombination with the increase of Be doping density.

Metamorphic InAs1-xBix/In0.83Al0.17As quantum well structures on InP for mid-infrared emission

This work reports on InP-based metamorphic quantum well structures with bismuth incorporation for mid-infrared applications. InAs1-xBix quantum well structures have been grown on InP-based metamorphic In0.83Al0.17As buffers and photoluminescence beyond 3.1 μm has been achieved at 300 K, which is longer than the referenced InAs quantum well. X-ray diffraction, cross-sectional transmission electron microscopy, and energy dispersive X-ray spectroscopy measurements reveal clear interfaces of InAsBi quantum well with low bismuth, while more defects and bismuth inhomogeneity were observed as more bismuth was incorporated.

Electron-initiated low noise 1064 nm InGaAsP/InAlAs avalanche photodetectors

We report an electron-initiated 1064 nm InGaAsP avalanche photodetectors (APDs) with an InAlAs multiplier. By utilizing a tailored digital alloy superlattice grading structure, a charge layer and a p type InAlAs multiplier, an unity gain quantum efficiency of 48%, a low room temperature dark current of 470 pA at 90% breakdown voltage, and a low multiplication noise with an effective k ratio of ∼0.2 are achieved. The measured maximum gain factor is 5 at room temperature, which is currently limited by the non-optimized electric field profiles, and can be readily enhanced by modifying the doping and thickness parameters for the multiplier and the charge layer.

Surface and optical properties of silicon nitride deposited by inductively coupled plasma-chemical vapor deposition

The surface and optical properties of silicon nitride samples with different compositions were investigated. The samples were deposited on InP by inductively coupled plasma chemical vapor deposition using different NH3 flow rates. Atomic force microscopy measurements show that the surface roughness is increased for the samples with both low and high NH3 flow rates. By optimization, when the NH3 flow rate is 6 sccm, a smooth surface with RMS roughness of 0.74 nm over a 5 × 5 μm2 area has been achieved. X-ray photoelectron spectroscopy measurements reveal the Si/N ratio of the samples as a function of NH3 flow rate. It is found that amorphous silicon is dominant in the samples with low NH3 flow rates, which is also proved in Raman measurements. The bonding energies of the Si and N atoms have been extracted and analyzed. Results show that the bonding states of Si atoms transfer from Si0 to Si+4 as the NH3 flow rate increases.

Bismuth for tailoring and modification of InP-based detector and laser structures in 2–3 µm band

The effects of bismuth on the performances of InP-based detectors and multiple triangular quantum wells in 2-3 μm band have been investigated. The cut-off wavelength of the InGaAsBi detector is tailored to 2.1 μm by the bismuth incorporation in the absorption layer, but the detector still shows an encouraging dark current due to decreased lattice mismatch to InP substrate. The material quality of the InAs/InGaAs triangular quantum wells has been significantly improved by introducing bismuth as a surfactant during growth. The moderate bismuth reduces the surface roughness, improves the heterostructure interfaces and enhances the photoluminescence intensity obviously, whereas deterioration occurs in the case of excessive bismuth flux. Bismuth shows a promising potential to improve InP-based detector and laser structures both by incorporating into the alloys and acting as a surfactant.

Characteristics of InGaAsBi with various lattice mismatches on InP substrate

To develop bismuth-containing infrared optoelectronic devices, InGaAsBi/InP films with different lattice mismatches have been investigated. The lattice mismatch was tailored by changing the Bi content in conjunction with the In content simultaneously. X-ray diffraction analysis revealed that alloy lattice constants have been extended positively by incorporation of Bi into the crystal lattice. Electrical and optical characteristics were investigated by Hall-effect, optical absorption and photoluminescence measurements. A bandgap shrinking of about 56.4 meV/Bi% was deduced by X-ray diffraction and optical absorption measurements. From the excitation dependent photoluminescence measurement at 10 K, the donor-acceptor pair emissions were inferred for samples containing moderate and high levels of Bi. The temperature dependence of the PL peak energy is as small as 0.06 meV/K in In0.5Ga0.5As0.987Bi0.013, which is fairly low compared with that of In0.5Ga0.5As.