P.H Zhang

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...

Band gap narrowing effect in Be-doped AlxGa1−xAs studied by photoluminescence spectroscopy

Abstract The energy band gap narrowing (BGN) as a function of doping concentration in Be-doped Al 0.33 Ga 0.67 As is investigated using photoluminescence (PL) measurements on samples grown by molecular beam epitaxy (MBE). An expression for theoretically predicting the band gap narrowing has been deduced for p-type doping in Al x Ga 1−x As (0≤x≤0.45). The experimental results obtained from the PL spectra are in good agreement with this expression. A simple empirical relation for the PL peak energy of Be-doped Al 0.33 Ga 0.67 As as a function of carrier concentration is also presented. This provides a convenient way of determining the carrier concentration in Be-doped Al 0.33 Ga 0.67 As samples nondestructively.

Electrical and optical properties of InP grown by molecular beam epitaxy using a valved phosphorus cracker cell

Abstract We report the molecular beam epitaxial (MBE) growth of high quality epitaxial indium phosphide (InP) using a valved phosphorus cracker cell over a wide range of V/III flux ratio (1.2–9.3) and substrate temperature (360°C to 500°C). The as-grown epitaxial InP on InP (100) substrate was n-type, with a background electron concentration and mobility which varied according to the V/III flux ratio and substrate temperature ( T s ). Using a cracking zone temperature ( T cr ) of 850°C, the highest electron mobility at 77 K of 40 900 cm 2 /Vs was achieved at a V/III flux ratio of 2.3 at a substrate temperature of 440°C. The corresponding background electron concentration at 77 K was the lowest at 1.74×10 15 cm −3 . The photoluminescence (PL) full-width at half maximum (FWHM) decreased significantly in samples grown at lower flux ratios indicating an improvement in the optical quality.

Electrical and optical characteristics of molecular beam epitaxial Be-doped In0.53Ga0.26Al0.21As layers grown lattice-matched on InP (100) substrates

Abstract This paper reports the effects of beryllium (Be) doping in In 0.53 Ga 0.26 Al 0.2 As layers grown lattice-matched to InP (100) substrates by molecular beam epitaxy (MBE). Hall effect measurements showed that hole concentrations as high as 2.94×10 19 cm −3 was achieved, and the concentration decreased with further increase in the Be cell temperature. Depending on the hole concentration, good optical quality was achieved as verified by photoluminescence (PL) measurements. X-ray diffraction (XRD) measurements showed lattice mismatch values of lower than 8.6×10 −4 in most samples. An intense PL peak (5 K) at 1.089 eV which is attributed to band-acceptor recombination was observed from the sample with the lowest hole concentration of 2.28×10 16 cm −3 . This sample exhibited the lowest PL full-width at half maximum (FWHM) of 8 meV (at 5 K) for the free exciton recombination. To the best of our knowledge, this is the lowest value reported to date. An increase in the hole concentration caused a merging of the band-acceptor and free excitor recombination lines to form a broad PL spectrum. A shift in the free exciton peak position in the PL spectrum was observed following an increase in the hole concentration, an effect which was probably due to degeneracy.

Nondestructive determination of beryllium outdiffusion in AlGaAs/GaAs heterojunction bipolar transistor structures by low-temperature photoluminescence

In this work, low-temperature photoluminescence (PL) is used for the investigation of beryllium (Be) dopant outdiffusion in AlGaAs/GaAs single-heterojunction bipolar transistors (HBTs). Near the typical emission peak at ∼1.92 eV which is due to the band-to-band transition from AlGaAs emitter, an additional emission peak is found in the PL spectrum. This peak is found to be caused by the Be-related transition from AlGaAs emitter due to the Be outdiffusion from the GaAs base to the AlGaAs emitter. The concentration of Be outdiffused into the emitter can be estimated from the energy separation between these two emission peaks in AlGaAs range based on the band gap narrowing effect. The measured dc current gain and the emitter-base turn-on voltage of the HBTs fabricated on different wafers with different growth conditions were found to correlate well with the PL results. Our results demonstrate that low temperature PL technique is an efficient method in identifying Be outdiffusion in HBTs and is useful in HBT growth and device structure optimization.

V/III ratio effects on the growth of In1−x−yGaxAlyAs on InP substrates by molecular beam epitaxy

In this paper, we report the effects of arsenic pressure (V/III ratio) on the properties of undoped In 1-x-y Ga x Al y As layers grown by molecular beam epitaxy (MBE) on InP(100) substrates. The quaternary samples were analysed using double-axis X-ray diffraction (XRD) and low-temperature photoluminescence (PL). XRD analysis showed that the lattice mismatch was relatively insensitive to flux ratio variations within the range investigated (V/III from 14 to 73). PL full width at half-maximum (FWHM) as low as 12.7 meV (at 5 K), a value which is comparable to the best reported, was achieved at a V/III ratio = 33. The PL and XRD FWHMs broadened significantly as the V/III ratio was decreased below 21 or increased above 50. Within the range investigated, the optimum V/III ratio for the growth of InGaAlAs layers was found to be 21-50. The effect of the V/III ratio on the optical and crystalline properties was explained in terms of clustering, which was characterized by analysing the difference between the PL peak energy and the band-gap energy calculated from XRD compositional measurements. 1998 Published by Elsevier Science Ltd. All rights reserved.

Effect of growth interruption on the electrical and optical characteristics of InP/InGaAs HEMT structures

Abstract The effect of growth interruption on the top interface of the InGaAs layer in InP/In 0.53 Ga 0.47 As/InP heterostructures grown by molecular beam epitaxy was studied by Hall measurements, photoluminescence (PL) spectroscopy and high-resolution X-ray diffraction (HR-XRD). PL results from multiple quantum well structures (three stacked InGaAs quantum wells of 10, 20 and 40 A width lattice matched to 300 A InP barriers) indicated an optimum interruption time of ∼70 s for obtaining the minimum PL line width. Lattice matched high-electron mobility transistor structures were grown using different growth interruption times similar to MQW structures. A maximum electron mobility of 3500 cm 2 /V s and 15 900 cm 2 /V s at 300 K and 77 K, respectively, was measured. This time approximately corresponds to the minimum PL line width obtained for the quantum well structure. The variation of the electron mobility with the growth interruption time was attributed to the formation of a thin InAsP or InGaAsP layer on the surface of the InGaAs at the InGaAs/InP heterointerface similar to MOVPE-grown samples. PL and HR-XRD results indicate that a similar phenomenon may be operative in MBE-grown layers also, and an optimum interruption time may provide abrupt interfaces with better electrical and optical properties.

Molecular beam epitaxial growth of InP using a valved phosphorus cracker cell: optimization of electrical, optical and surface morphology characteristics

We report the molecular beam epitaxial (MBE) growth of epitaxial InP using a valved phosphorous cracker cell at a range of cracking zone temperature (T/sub cr/=875/spl deg/C to 950/spl deg/C), V/III flux ratio (V/III=1.2 to 9.3) and substrate temperature (T/sub s/=360/spl deg/C to 500/spl deg/C). The as-grown epitaxial InP on InP [100] substrate was found to be n-type from Hall measurements. The background electron concentration and mobility exhibited a pronounced dependence on the cracking zone temperature, V/III flux ratio and substrate temperature. Using a cracking zone temperature of 850/spl deg/C, the highest 77 K electron mobility of 40900 cm/sup 2//Vs was achieved at a V/III ratio of 2.3 at substrate temperature (T/sub s/) of 440/spl deg/C. The corresponding background electron concentration was 1.74/spl times/10/sup 15/ cm/sup -3/. The photoluminescence (PL) spectra showed two prominent peaks at 1.384 eV and 1.415 eV, with the intensity of the low energy peak becoming stronger at higher cracking zone temperatures. The lowest PL FWHM achieved at 5 K was 5.2 meV.