K. L. Lew

High-speed picosecond pulse response GaNAsSb p-i-n photodetectors grown by rf plasma-assisted nitrogen molecular beam epitaxy

The authors report on picosecond pulse response GaNAsSb∕GaAs p-i-n photodetectors grown by molecular beam epitaxy in conjunction with a rf plasma-assisted nitrogen source. The 2μm thick GaNAsSb photoabsorption layer contains 3.3% of N and 8% of Sb resulting in a dc photoresponse up to 1380nm wavelength. Dark current densities at 0 and −5V are 1.6×10−5 and 13A∕cm2, respectively. The GaNAsSb photodiodes exhibit a record pulse response width of only 40.5ps (full width at half maximum) corresponding to a 4.5GHz bandwidth.

Effect of growth temperature on defect states of GaAsSbN intrinsic layer in GaAs∕GaAsSbN∕GaAs photodiode for 1.3μm application

A GaAsSbN layer closely lattice matched to GaAs was used as an intrinsic layer (i layer) in a GaAs∕GaAsSbN∕GaAs p-i-n photodiode with response up to 1.3μm. Deep level transient spectroscopy measurement on the GaAs∕GaAsSbN∕GaAs reveals two types of hole traps (HTs) in the GaAsSbN i layer; (i) HT1: a shallow N-related defect state (Ea∼0.10–0.12eV) and (ii) HT2: an AsGa point defect-related midgap defect state with Ea∼0.42–0.43eV. Reduction in growth temperature from 480to420°C reduces the HT2 trap concentration from 4×1015to1×1015cm−3, while increases the HT1 trap concentration from 1×1014to7×1014cm−3. Reduction in the HT2 trap concentration following growth temperature reduction was attributed to the suppression of AsGa point defect formation. Evidence of possible change of the AsGa midgap state to a shallow level defect due to the formation of (AsGa–NAs) pairs was also suggested to have increased the HT1 trap concentration and reduced the HT2 trap concentration. An ∼4dBm improvement in photoresponse under...

Defect-induced trap-assisted tunneling current in GaInNAs grown on GaAs substrate

We present the reverse-bias current-voltage and deep-level transient spectroscopy (DLTS) characteristics of a Ga0.90In0.10N0.033As0.967∕GaAs positive-intrinsic-negative photodiode (Eg=0.92 eV) and a trap-assisted tunneling model which considers generation-recombination and tunneling mechanisms. Using trap parameters obtained from the DLTS measurement, the model generates current-voltage characteristics of the photodiode, which were found to be in good agreement with experimental current-voltage curves at different temperature. The model also suggests that high dark current at low reverse-bias voltage is caused by the presence of traps which have low activation energy. Furthermore, it is predicted that approximately ten times reduction in the dark current can be achieved when the trap concentration of type H-1 (Ea=0.15 eV) is reduced by one order. On the other hand, a similar reduction in defect concentration of type H-2 (Ea=0.40 eV), which is nearer to midgap does not produce the same effect.

Electroluminescence and structural characteristics of InAs/In0.1Ga0.9As quantum dots grown on graded Si1−xGex/Si substrate

We studied the electroluminescence and structural characteristics of five-layer stacked self-assembled InAs/In0.1Ga0.9As quantum dot (QD) structures grown on graded Si1−xGex/Si substrate. The QD was found to take on a lens shaped structure with aspect ratio of 0.23±0.05. Room-temperature electroluminescence at 1.29 μm was observed from the QD structures. The external quantum efficiency as function of injected current was investigated and the dominant carrier recombination processes were identified from analysis of the current-optical power relationship.

High responsivity GaNAsSb p-i-n photodetectors at 1.3µm grown by radio-frequency nitrogen plasma-assisted molecular beam epitaxy

GaNAsSb/GaAs p-i-n photo notdetectors with an intrinsic GaNAsSb photoabsorption layer grown at 350 degrees C, 400 degrees C, 440 degrees C and 480 degrees C, have been prepared using radio-frequency nitrogen plasma-assisted molecular beam epitaxy in conjunction with a valved antimony cracker source. The i-GaNAsSb photoabsorption layer contains 3.3% of nitrogen and 8% of antimony, resulting in DC photo-response up to wavelengths of 1350 nm. The device with i-GaNAsSb layer grown at 350 degrees C exhibits extremely high photoresponsivity of 12A/W at 1.3 microm. These photodetectors show characteristics which strongly suggest the presence of carrier avalanche process at reverse bias less than 5V.

High gain AlGaAs∕GaAs heterojunction bipolar transistor fabricated on SiGe∕Si substrate

High gain AlGaAs∕GaAs heterojunction bipolar transistors grown on SiGe∕Si substrate have been fabricated. Measured peak dc current gain of ∼100 is obtained for a device with emitter area of ∼1.6×103μm2, with base concentration of 1×1019cm−3. The dominant base current component is discussed and determined. The breakdown characteristic is studied and compared with that of the device grown on GaAs substrate. Our experimental results demonstrate that SiGe∕Si substrate could provide a robust method for monolithic integration of high speed GaAs-based electronic devices with silicon-based circuitry.

Study of surface microstructure origin and evolution for GaAs grown on Ge/Si1−xGex/Si substrate

The origin and evolution of surface microstructures in the GaAs layer grown on the Ge/Si1−xGex/Si substrate were studied. The characteristic surface microstructures are formed in pairs. By correlating the results from atomic force microscopy and cross-sectional transmission electron microscopy characterization, these paired surface microstructures are identified as { 111 } stacking faults that propagate at 54 ◦ with respect to the substrate surface. The stacking faults originate from the single-stepped GaAs/Ge heterointerface, as a consequence of in situ annealing of the Ge surface. The surface microstructure density becomes lower and the mean lateral size larger when the GaAs thickness is increased from 0.54 to 1.11 µm. (Some figures in this article are in colour only in the electronic version)

Model for InGaP/GaAs/InGaP double heterojunction bipolar transistor

The current–voltage characteristics of an InGaP/GaAs/InGaP double heterojunction bipolar transistor (DHBT) are modeled where the tunneling effect at the base–collector (B–C) junction and base–emitter (B–E) junction is taken into account. Therefore, this model can be applied to both conventional DHBT and composite collector heterojunction bipolar transistor. The role of the n−GaAs layer and n+InGaP layer are discussed and the effects of variation in the doping level and thickness of these layers are considered in the model. Good agreement between our predictions of the model and reported experimental results is achieved.The current–voltage characteristics of an InGaP/GaAs/InGaP double heterojunction bipolar transistor (DHBT) are modeled where the tunneling effect at the base–collector (B–C) junction and base–emitter (B–E) junction is taken into account. Therefore, this model can be applied to both conventional DHBT and composite collector heterojunction bipolar transistor. The role of the n−GaAs layer and n+InGaP layer are discussed and the effects of variation in the doping level and thickness of these layers are considered in the model. Good agreement between our predictions of the model and reported experimental results is achieved.

1.55μm GaAs∕GaNAsSb∕GaAs optical waveguides grown by radio frequency nitrogen plasma-assisted molecular beam epitaxy

We demonstrate a 1.55μm GaAs∕GaNAsSb∕GaAs optical waveguide grown by molecular beam epitaxy as an alternative to the AlGaAs∕GaAs system. The 0.4-μm-thick GaNAsSb guiding layer contains ∼3.5% of N and 9% of Sb, resulting in optical band gap of 0.88eV. The refractive index of the GaNAsSb layer was measured from 800to1700nm. The GaNAsSb layer has a refractive index value of 3.42 at 1.55μm wavelength. The propagation loss measured using the Fabry–Perot resonance method was found to be affected by nitrogen-related defect absorption.

Effect of composite collector design on the breakdown behavior of InGaP/GaAs double heterojunction bipolar transistor

A series of experiments and calculations has been carried out to study the effect of different composite collector designs on InGaP/GaAs/InGaP double heterojunction bipolar transistor breakdown characteristics. A comparison between uncorrected and dead-space corrected models was carried out, and it was found that the dead-space effect is dominant for collector thickness below 300 nm. However, this effect can be neglected for collector thickness larger than 500 nm. The role of lightly doped GaAs (n−-GaAs) and heavily doped InGaP (N+-InGaP) spacer layers is discussed systematically to establish a criterion for designing the composite collector structure. The experimental and theoretical results show that it is necessary to keep the sum of n−-GaAs and N+-InGaP spacer layer thickness below 50 nm to avoid significant degradation of the device breakdown characteristics.