H H Gao

Room-temperature InAs0.89Sb0.11 photodetectors for CO detection at 4.6 μm

An InAs0.89Sb0.11 photovoltaic detector that operates at room temperature in the 2.5-5 mu m mid-infrared wavelength region is reported. The photodiode has an extended spectral response compared with other currently available III-V room-temperature detectors. In order to accommodate the large lattice mismatch between the InAs0.89Sb0.11 active region and the InAs substrate, a buffer layer with an intermediate composition was introduced into the structure. In this way, we obtained room-temperature photodiodes with a cutoff wavelength near 5 mu m, a peak responsivity of 0.8 A/W, and a detectivity of 1.26 x 10(9) cm Hz(1/2)/W. These devices could be effectively used as the basis of an optical sensor for the environmental monitoring of carbon monoxide at 4.6 mu m, or as a replacement for PbSe photoconductors

Purification of epitaxial InAs grown by liquid phase epitaxy using gadolinium gettering

Very pure InAs epitaxial layers of high quantum efficiency have been grown by liquid phase epitaxy using Gd gettering of the growth solution. The residual carrier concentration was reduced to ∼6×1015 cm−3 and the peak photoluminescence intensity increased considerably (between 10 and 100 times) using this technique. The low-temperature (4 K) photoluminescence spectra exhibited sharp bound exciton and donor-acceptor lines. The linewidth of the exciton was measured to be only 3.8 meV which is narrower than for undoped epitaxial InAs grown by other techniques.

High power 4.6 µm light emitting diodes for CO detection

We report on a powerful 4.6 ?m light emitting diode (LED), operating at room temperature, suitable for carbon monoxide gas detection. The source is based on a InAs0.55Sb0.15P0.30 /InAs0.89Sb0.11/InAs0.55Sb0.15P0.30 symmetrical double heterostructure with large band offsets. To improve performance, the InAs0.89Sb0.11 ternary material in the active region was purified by using rare-earth ion gettering during liquid phase epitaxial growth. A pulsed optical output power in excess of 1 mW at room temperature has been measured, making these emitters suitable for use in cost-effective instruments for the environmental monitoring of carbon monoxide. The Auger coefficient of the InAs0.89Sb0.11 active region material was evaluated by analysis of the temperature quenching of the LED output power measured at constant current. It was found to be C0 = 1.5 ? 10-26 cm6 s-1 with an activation energy of E = 31 meV, which is in good agreement with previous findings in the literature.

A room temperature photovoltaic detector for the mid-infrared (1.8-3.4 m) wavelength region

In this paper, we report on an (pin) photovoltaic detector operating in the mid-infrared spectral region. Basic detector characteristics have been measured and compared with other detectors in this wavelength range. The typical detectivity of the photodiodes is cm at room temperature, which compares very favourably with that of TE cooled HgCdTe and is at least three times that of cooled PbSe photoconductors over the same wavelength range. The heterojunction photodiodes offer the advantage of increased sensitivity and extended wavelength response at room temperature compared with that of currently available commercial photodetectors, making them an attractive alternative for a number of mid-infrared applications including optical gas sensors and infrared spectrometers. The heterojunction photodiodes were grown on p type (100) InAs substrates by liquid phase epitaxy (LPE). Several different device structures were fabricated and compared in order to investigate the dependence of dark current on doping concentration and layer structure, with a view towards device optimization. It was found that at room temperature the dark current is dominated by bulk leakage (minority carrier diffusion) rather than other mechanisms, such as mismatch dislocation or surface leakage. We established that the main reasons why the properties of these heterojunction photodiodes are for superior to those of more conventional detectors including homojunction InAs photodiodes are (a) that the wider-bandgap layer has a lower equilibrium population of thermionic minority carriers which contribute to the diffusion current, resulting in lower leakage, and (b) the structure has a transparent window layer allowing better capture of photons in the active region.

A novel LED module for the detection of H2S at 3.8 µm

A new type of mid-infrared LED module (LEDM) operating at 3.8 mu m is reported. The device was produced using liquid phase epitaxy (LPE) and consists of a series array of four individual LED chips. Electro-optic characteristics of the devices were measured and are reported here. The output power from the module was measured to be as high as 8 mW at room temperature under pulsed drive conditions. Compared with previous results our LED and LEDM devices represent a considerable improvement in output power at 3.8 mu m. The reasons for this improvement are related to the purification techniques used in the LPE growth procedure and the de-tuning of the CHSH Auger resonance in the InAs0.95Sb0.05 alloy which forms the active region. The peak in the electroluminescence emission spectrum was found to be co-incident with the absorption band of H2S gas and as such we were able to demonstrate substantial optical absorption which clearly shows the potential application of such devices in infrared gas sensor instrumentation.

High quality InAs grown by liquid phase epitaxy using gadolinium gettering

In this paper, we report the growth of very pure InAs epitaxial layers of high quantum efficiency, by introducing the rare-earth element Gd into the liquid phase during LPE growth. We find that the carrier concentration of InAs layers can be effectively reduced to . Also, the peak photoluminescence (PL) intensity of such layers can be considerably increased by between ten- and 100-fold compared with untreated material. We attribute this behaviour to the gettering of residual impurities and corresponding reduction of non-radiative recombination centres in the presence of Gd. Four intense sharp lines dominated the low temperature (4 K) photoluminescense spectra of Gd-treated InAs layers. The strongest two of these were found to originate from (a) bound excitons, and (b) donor-acceptor recombination, whereas the remaining two, (c) and (d), were associated with defect-related recombination. The linewidth (FWHM) of the exciton peak (a) was reduced to only 3.8 meV, which is narrower than for undoped epitaxial InAs grown by MBE or MOVPE.

InAsSb/InAsSbP light emitting diodes for the detection of CO and CO2 at room temperature

This report describes the epitaxial growth and fabrication of room-temperature InAs0.89Sb0.11/InAs0.48Sb0.22P0.30 semiconductor light emitting diodes operating in the mid-infrared wavelength region near 4.5 µm. The InAs0.89Sb0.11 ternary material used in the light emitting diode active region has a large lattice mismatch with respect to the InAs substrate layer and in order to accommodate this it was necessary to grow a buffer layer with an intermediate composition (InAs0.94Sb0.06). The devices exhibit infrared emission at 4.5 µm and could be effectively used as the basis of an optical sensor for the environmental monitoring of carbon monoxide at 4.6 µm and carbon dioxide at 4.2 µm in various applications.

Optical switching in midinfrared light-emitting diodes .

We report on the optical quenching of electroluminescence in midinfrared light-emitting diodes operating at 3.0 μm. The source is based on a symmetrical double heterostructure with large band offsets and is effectively switched off using coherent visible light.

Interface electroluminescence from InAs quantum well LEDs grown by rapid slider liquid phase epitaxy. .

Electroluminescence has been observed at 3.3 µm from InAs quantum well LEDs grown from the liquid phase for the first time. A special rapid slider liquid phase epitaxial growth technique was used to produce the wells within the active region of an InAsSbP homojunction p-i-n LED. The light emission was attributed to type II recombination between confined electron and hole states at the InAsSbP/ InAs interfaces of the InAs quantum well. Intense electroluminescence emission was observed at low temperatures from a multi-interface LED which contained three InAs quantum wells in the i-region of the LED structure with emission peaking at 3.68 µm at 250 K.