S.P. Xi

2.4 µm InP-based antimony-free triangular quantum well lasers in continuous-wave operation above room temperature

In this work, we report on the above-room-temperature continuous-wave operation of InP-based antimony-free triangular quantum well (QW) lasers emitting up to approximately 2.4 µm. X-ray diffraction measurement confirms the favorable structural quality of the highly strained triangular QWs composed of InAs/In0.53Ga0.47As digital alloy. The maximum continuous-wave working temperature reaches 340 K, and the output power at 300 K is about 11 mW/facet at an injection current of 350 mA. The internal quantum efficiency of 58% is deduced at 300 K, and the extrapolated threshold current density for infinite cavity length is 210 A/cm2 per quantum well.

Dark current suppression in metamorphic In0.83Ga0.17As photodetectors with In0.66Ga0.34As/InAs superlattice electron barrier

We report on InP-based metamorphic In0.83Ga0.17As photodetectors with dramatically suppressed dark currents by inserting a strain-compensated In0.66Ga0.34As/InAs superlattice electron barrier in the In0.83Ga0.17As absorption layer. Compared with a reference detector without the barrier, the device showed that the dark current is reduced by about half at room temperature and is more than two orders of magnitude at 77 K at low bias, while the responsivity remained unchanged. The generation recombination and tunneling currents are significantly suppressed, and the dark current remains diffusion-current-limited above 175 K. The dark current density at −10 mV is reduced to 3.95 nA/cm2 at 175 K.

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.

Low Operating Voltage and Small Gain Slope of InGaAs APDs With p-Type Multiplication Layer

We reported separate absorption and multiplication InAlAs/InGaAs avalanche photodiodes with a p-type multiplication layer. Wedge-shaped electric field profiles with different gradients and peak intensities confined in a thin InAlAs avalanche layer were realized. These devices showed optimum operating gains up to 40 in linear mode with low operating voltages <;20 V, small gain slopes, and high-gain uniformity. Moreover, a reduced breakdown voltage temperature coefficient <;6 mV/K in the temperature range of 200-350 K was observed, whereas the dark current showed a noticeable increase. Those multiplication performances are attributed to the modified electric field profiles and are ideally suitable for focal plane array imaging applications.

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.

Carrier scattering and relaxation dynamics in n-type In0.83Ga0.17As as a function of temperature and doping density

The carrier scattering and relaxation dynamics in an n-type In0.83Ga0.17As ternary alloy are investigated by measuring the temperature dependent electron Hall mobilities and the hole lifetimes as a function of doping density. The dominant scattering mechanisms in temperature ranges of T < 80 K, 80 < T < 120 K, and 120 < T < 300 K in lightly doped In0.83Ga0.17As are found to be impurity scattering, alloy disorder scattering and phonon scattering, respectively, while in heavily doped In0.83Ga0.17As alloy scattering dominates over the whole measured temperature range. By fitting the measured temperature dependent carrier lifetimes, the dominant carrier relaxation mechanisms in lightly doped In0.83Ga0.17As are identified to be the radiative recombination and the Shockley–Read–Hall effect for samples grown on InP and GaAs substrates, respectively. The lifetime in heavily doped In0.83Ga0.17As is below 10 ns with an Auger dominated recombination. Lastly, photoluminescence as well as the light absorption measurements are performed, showing that the grown lightly doped In0.83Ga0.17As has a high optical quality comparable to the lattice-matched In0.53Ga0.47As.

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.