Haiqun Zheng

Characterization of linearly graded metamorphic InGaP buffer layers on GaAs using high-resolution X-ray diffraction

High-resolution X-ray diffraction (HRXRD) was used to characterize linearly graded metamorphic InGaP buffer layers grown at different temperatures on GaAs substrate by solid-source molecular beam epitaxy. The sample grown at 380°C did not exhibit a Bragg diffraction peak corresponding to the top layers consisting of an InGaAs/InP single quantum-well structure, since it could not maintain a two-dimensional growth. When the samples were grown at higher temperatures (430–480°C), the top epitaxial layers were nearly fully relaxed and the strain relaxation anisotropy in two 〈110〉 directions was found to be small. It was also found that the growth temperature of the buffer layer for these samples did not influence the strain relaxation ratio. Moreover, the full width at half maximum (FWHM) values of the XRD peaks suggest that the sample grown at 480°C has better material quality.

Demonstration of aluminum-free metamorphic InP/In/sub 0.53/Ga/sub 0.47/As/InP double heterojunction bipolar transistors on GaAs substrates

We report, for the first time, the successful fabrication of aluminum-free metamorphic (MM) InP/In/sub 0.53/ Ga/sub 0.47/ As/InP double heterojunction bipolar transistors (DHBTs) on GaAs substrates with a linearly graded In/sub x/Ga/sub 1-x/P buffer grown by solid-source molecular beam epitaxy (SSMBE). Devices with 5/spl times/5 /spl mu/m/sup 2/ emitters display a peak current gain of 40 and a common-emitter breakdown voltage (BV/sub CE0/) higher than 9 V, a current gain cut-off frequency (f/sub T/) of 48 GHz and a maximum oscillation frequency (f/sub max/) of 42 GHz. A minimum noise figure of 2.9 dB and associated gain of 19.5 dB were measured at a collector current level of 2.6 mA at 2 GHz. Detailed analysis suggests that the degradation of the base-emitter heterojunction interface and the increase of bulk recombination are the most probable causes for the poorer device performance of current metamorphic HBTs compared with lattice-matched HBTs.

Metamorphic InP/InGaAs heterojunction bipolar transistors on GaAs substrate: DC and microwave performances

High-performance InP/In/sub 0.53/Ga/sub 0.47/As metamorphic heterojunction bipolar transistors (MHBTs) on GaAs substrate have been fabricated using In/sub x/Ga/sub 1-x/P strain relief buffer layer grown by solid-source molecular beam epitaxy (SSMBE). The MHBTs exhibited a dc current gain over 100, a unity current gain cutoff frequency (f/sub T/) of 48 GHz and a maximum oscillation frequency (f/sub MAX/) of 42 GHz with low junction leakage current and high breakdown voltages. It has also been shown that the MHBTs have achieved a minimum noise figure of 2 dB at 2 GHz (devices with 5/spl times/5 /spl mu/m/sup 2/ emitter) and a maximum output power of 18 dBm at 2.5 GHz (devices with 5/spl times/20 /spl mu/m/sup 2/ emitter), which are comparable to the values reported on the lattice-matched HBTs (LHBTs). The dc and microwave characteristics show the great potential of the InP/InGaAs MHBTs on GaAs substrate for high-frequency and high-speed applications.

Metamorphic In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistors on GaAs with InxGa1−xP graded buffer

A new metamorphic In0.52Al0.48As/In0.53Ga0.47As high electron mobility transistor (HEMT) structure was grown on a GaAs substrate with a InxGa1−xP graded buffer layer by solid-source molecular beam epitaxy. The In0.53Ga0.47As channel layer was grown on the InGaP buffer layer directly without an InAlAs buffer as in the conventional design. High-resolution x-ray diffraction reveals that the whole layer structure is nearly fully relaxed. Hall measurement showed that this new layer design exhibits higher electron mobility and carrier concentration as well as lower light sensitivity compared to the reference sample with the conventional design. The promising device performance demonstrates the potential of using this metamorphic HEMT device in high speed and high frequency applications.

Growth of self-organized InAs quantum dots on InP by solid-source molecular beam epitaxy

Self-organized InAs quantum dots (QDs) on InP (1 0 0) substrate have been prepared by solid-source molecular-beam epitaxy (SSMBE). Atomic force microscopy (AFM) examination shows that the InAs QDs possess low aspect ratio (1 : 17) of height vs. diameter. The low-temperature photoluminescence (PL) behavior of the QDs is characterized by a 65 meV PL linewidth at ∼0.8 eV, with three other emissions, which correspond to the various thicknesses of InAs wetting layers. It is deduced that the InAs wetting layers exceeded the intended InAs deposition, which is attributed to unintentional As/P exchange reaction. This excess material is further confirmed by XRD measurements, and indicates that effective exchange occurs even at low temperature (500°C) for SSMBE growth. No significant change in the QD emission peak is observed in the sample grown at high temperature, indicating the absence of any significant As/P exchange reaction in the QDs.

A comprehensive study of AlGaAs/GaAs beryllium- and carbon-doped base heterojunction bipolar transistor structures subjected to rapid thermal processing

AlGaAs/GaAs single heterojunction bipolar transistor (HBT) structures with Be- and C-doped bases have been annealed at different temperatures using rapid thermal processing (RTP). Both electrical and low-temperature photoluminescence measurements were used to investigate their thermal stability. We found that the conventional AlGaAs/GaAs abrupt HBT structures could undergo significant degradation at temperatures commonly encountered in typical RTP for device fabrication. The decrease of current gain was observed in both molecular beam epitaxy-grown HBTs with a Be-doped base and metalorganic chemical vapor deposition-grown HBTs with a C-doped base after RTP at temperatures greater than 600 °C. Our studies show that high-temperature RTP could induce undesirable degradation in AlGaAs/GaAs HBTs. Different degradation mechanisms, which are similar to those for the degradation of the Be- and C-doped base HBTs under current-induced stress, are responsible for the degradation of the Be- and C-doped HBTs subjected...

Effect of rapid thermal annealing on InGaAs/GaAs quantum wells

We have studied the effect of rapid thermal annealing (RTA) on highly strained InGaAs/GaAs quantum wells by using photoluminescence (PL) and double-crystal X-ray diffraction (DCXRD) measurements. It is found that a distinct additional PL emission peak can be observed for the annealed samples. This PL emission possesses features similar to the PL emission from InGaAs/GaAs quantum dots (QDs) with the same indium content. It is proposed that this emission stems from QDs, which were formed during the annealing process. This formation is attributed to the favorable diffusion due to the inhomogeneous strain distribution in the InGaAs layer intersurface. The DCXRD measurements also confirm that the dominant relaxation is strain enhanced diffusion under the low annealing temperatures.

DC Characterization of Metamorphic InP/InGaAs Heterojunction Bipolar Transistors at Elevated Temperature

A detailed DC characterization of metamorphic InP/InGaAs/InP double heterojunction bipolar transistors (DHBTs) in the temperature range of 300 K to 400 K was carried out and the carrier transport properties were investigated. Our experiments reveal that band-to-band recombination is the dominant mechanism for the base current indicating the good base material quality for the metamorphic HBT structures.

Microwave noise and power performance of metamorphic InP heterojunction bipolar transistors

For the first time, microwave noise and power performance of metamorphic InP HBTs (MM-HBTs) grown on GaAs substrates are reported. We find that microwave performance of MM-HBTs are comparable to that of lattice-matched InP HBTs (LM-HBTs) of identical design but fabricated on an InP substrate. The preliminary results imply that the superior performance of InP HBTs can be confidently exploited with the more mature manufacturing technology of GaAs.

Device performance and transport properties of high gain metamorphic InP/InGaAs heterojunction bipolar transistors at elevated temperature

A detailed DC characterization of metamorphic InP/InGaAs/InP DHBTs in the temperature range of 300 K to 400 K was carried out and the carrier transport properties were investigated. Our experiments reveal that band-to-band recombination is the dominant mechanism for the base current indicating the good base material quality for the metamorphic HBT structures.