type-I Band Lineup Research Articles

Systematic study on dynamic atomic layer epitaxy of InN on/in +c-GaN matrix and fabrication of fine-structure InN/GaN quantum wells: Role of high growth temperature

The growth kinetics and properties of nominally 1-ML (monolayer)-thick InN wells on/in +c-GaN matrix fabricated using dynamic atomic layer epitaxy (D-ALEp) by plasma-assisted molecular beam epitaxy were systematically studied, with particular attention given to the effects of growth temperature. Attention was also given to how and where the ∼1-ML-thick InN layers were frozen or embedded on/in the +c-GaN matrix. The D-ALEp of InN on GaN was a two-stage process; in the 1st stage, an “In+N” bilayer/monolayer was formed on the GaN surface, while in the 2nd, this was capped by a GaN barrier layer. Each process was monitored in-situ using spectroscopic ellipsometry. The target growth temperature was above 620 °C and much higher than the upper critical epitaxy temperature of InN (∼500 °C). The “In+N” bilayer/monolayer tended to be an incommensurate phase, and the growth of InN layers was possible only when they were capped with a GaN layer. The InN layers could be coherently inserted into the GaN matrix under self-organizing and self-limiting epitaxy modes. The growth temperature was the most dominant growth parameter on both the growth process and the structure of the InN layers. Reflecting the inherent growth behavior of D-ALEp grown InN on/in +c-GaN at high growth temperature, the embedded InN layers in the GaN matrix were basically not full-ML in coverage, and the thickness of sheet-island-like InN layers was essentially either 1-ML or 2-ML. It was found that these InN layers tended to be frozen at the step edges on the GaN and around screw-type threading dislocations. The InN wells formed type-I band line-up heterostructures with GaN barriers, with exciton localization energies of about 300 and 500 meV at 15 K for the 1-ML and 2-ML InN wells, respectively.

Growth characteristics of corundum-structured α-(AlxGa1−x)2O3/Ga2O3 heterostructures on sapphire substrates

We report improved growth conditions for corundum-structured α-(AlxGa1−x)2O3, followed by the growth characteristics of α-(AlxGa1−x)2O3/Ga2O3 heterostructures with the use of mist chemical vapor deposition (CVD) technology. Higher growth temperatures, 700–800°C, were effective for better crystalline quality especially for higher Al composition x. Coherent growth of α-(AlxGa1−x)2O3 was achieved for x=0.03 and 0.11 with the film thickness of about 100nm. The type-I band lineup was expected for the heterostructure.

Mid-wave infrared HgCdTe nBn photodetector

A unipolar, barrier-integrated HgCdTe nBn photodetector with all n-type doping and a type-I band lineup is experimentally demonstrated. Planar mid-wave infrared (MWIR) nBn devices exhibit current-voltage (I-V) characteristics that are consistent with band inversion in reverse bias, indicating a barrier-influenced behavior. Dark current saturation is observed beyond a reverse bias of approximately −0.8 V. Bias-dependent photoresponse is observed in the mid-wave infrared with a cut-off wavelength around 5.7 μm. Numerical modeling based on experimental results predicts an internal peak quantum efficiency of approximately 66%.

Room temperature photoluminescence of high density (In,Ga)As/GaP quantum dots

We report on the achievement of high density (In,Ga)As self-assembled quantum dots on GaP substrate with a good homogeneity. Good structural and electronic properties have been achieved, as revealed by room temperature photoluminescence measurements and by comparison to both InAs/GaAs and InAs/InP materials reference systems. This is supported by atomistic calculations where the indium incorporation in InGaAs/GaP quantum structures is found to enhance both the type-I bandlineup and direct bandgap properties. The photoluminescence temperature dependence of the bandgap evidences the quantum confinement effects. Our results provide a valid framework to implement silicon optical devices based on InGaAs/GaP nanostructures.

Low Surface Recombination in InAlAs/InGaAsSb/InGaAs Double Heterojunction Bipolar Transistors

The surface recombination behavior of a series of InAlAs/InGaAsSb/InGaAs heterojunction bipolar transistors (HBTs) is investigated. It is found that the InGaAsSb base HBTs have lower emitter periphery surface recombination current density (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SURF</sub> ) than the HBT with an InGaAs base. It is attributed to the type-I band lineup at the B-E junction and the surface pining of the antimonide base layer. A lower S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is deduced for the DHBT with a higher Sb content in the InGaAsSb base.

Band lineup of pseudomorphic GaAs1−xSbx quantum-well structures with GaAs, GaAsP, and InGaP barriers grown by metal organic chemical vapor deposition

We report the growth of thin pseudomorphic GaAs1−xSbx (x∼0.3) quantum-well heterostructures by metal-organic chemical vapor deposition and the measurement of the band lineups for the heterointerface of GaAs1−xSbx (x∼0.3) quantum wells with GaAs, GaAs0.86P0.14, and In0.5Ga0.5P quantum-well barriers for 80Å double-quantum-well heterostructures using excitation-dependent cathodoluminescence measurements at 10K. GaAs1−xSbx (x∼0.3) quantum wells with GaAs and GaAs0.86P0.14 barriers show type-II band alignment, while GaAs1−xSbx (x∼0.3) quantum wells with In0.5Ga0.5P barriers exhibit a type-I band lineup. The type-I/type-II band alignment boundary condition as a function of the GaAs1−xSbx quantum-well composition and of the barrier materials and compositions is calculated. The pseudomorphic GaAs1−xSbx∕GaAs quantum-well heterointerface is estimated to have a type-II alignment. For GaAs1−xSbx∕GaAsP and GaAs1−xSbx∕InGaP heterostructures, both type-I and type-II alignments can occur depending on the quantum-well and barrier compositions. As the Sb composition of the quantum well increases, higher P alloy composition (in GaAsP barriers) and Ga (in InGaP barriers) composition are required in order to make the type-II to type-I transition.

Properties of GaAsSb QW Heterostructures Having Various Barrier Materials Grown by Metalorganic Chemical Vapor Deposition

ABSTRACTPseudomorphic GaAs1-xSbx quantum-well (QW) structures grown on GaAs substrates by metalorganic chemical vapor deposition (MOCVD) have been studied with various barrier materials to investigate the energy band lineup. To determine the band lineup of these structures, we have performed low-temperature current-dependent cathodoluminescence (LT-CL) measurements at 10K. For the structure with GaAs barriers, the data show strong evidence of Type-II staggered band lineup, which means that holes are confined in the valence band heavy-hole level of the GaAs1-xSbx quantum well and electrons are confined in the conduction band of the GaAs barrier.For the InGaP barriers, however, we observed only one peak that is related to transitions of a Type-I band lineup. From the LT-CL results, we find that the valence-band discontinuity ratio (Qv) between the GaAs0.73Sb0.27 double quantum wells (DQWs) and the GaAs barriers is ∼1.20. Furthermore, to improve the carrier confinement, we propose that InGaP barriers provide a Type-I band lineup with the GaAsSb QW.

Optical properties of ZnMgSeTe quaternary alloys grown on ZnTe substrates by molecular-beam epitaxy

Zn 1−x Mg x Se y Te 1−y quaternary alloys are grown on ZnTe(001) substrates for the first time. The photoluminescence properties of ZnMgSeTe are characterized by strong excitonic luminescence intensity with a narrow linewidth that indicate the high crystal quality and the composition homogeneity. It is deduced that the composition homogeneity of the alloy is originated from the stable sticking coefficient of group-VI species and the exclusion of impurity diffusion from the substrate. Type-I band lineup in the ZnTe/ZnMgSeTe single quantum well is estimated from the narrow and strong exciton luminescence line of the quantum well, and the band offset in this heterostructure is estimated based on the photoluminesence, photoluminescence excitation, and reflectance results as 20δEc:80δEv.

Band Line-up of InAsP/InAlGaAs Quantum Well

A band line-up of InAs0.45P0.55/In0.53(AlxGa1-x)0.47As heterojunction was investigated. Type-I and type-II band line-ups were obtained according to the Al relative composition x of InAlGaAs. This band line-up variation can be explained by assuming the conduction band discontinuity of InAsP/InP to be 0.35. A large conduction band discontinuity with type-I band line-up can be obtained with an Al relative composition x larger than 0.6 in this material system, which is promising for the multi-quantum well structure of 1.3-µm lasers with good temperature performance.

GaInNAs: a novel material for long-wavelength semiconductor lasers

GaInNAs was proposed and created in 1995 by the authors. It can be grown pseudomorphically on a GaAs substrate and is a light-emitting material having a bandgap energy suitable for long-wavelength laser diodes (1.3-1.55 /spl mu/m and longer wavelengths). By combining GaInNAs with GaAs or other wide-gap materials that can be grown on a GaAs substrate, a type-I band lineup is achieved and, thus, very deep quantum wells can be fabricated, especially in the conduction band. Since the electron overflow from the wells to the barrier layers at high temperatures can he suppressed, the novel material of GaInNAs is very attractive to overcome the poor temperature characteristics of conventional long-wavelength laser diodes used for optical fiber communication systems. GaInNAs with excellent crystallinity was grown by gas-source molecular beam epitaxy in which a nitrogen radical was used as the nitrogen source. GaInNAs was applied in both edge-emitting and vertical-cavity surface-emitting lasers (VCSELs) in the long-wavelength range. In edge-emitting laser diodes, operation under room temperature continuous-wave (CW) conditions with record high temperature performance (T/sub 0/=126 K) was achieved. The optical and physical parameters, such as quantum efficiency and gain constant, are also systematically investigated to confirm the applicability of GaInNAs to laser diodes for optical fiber communications. In a VCSEL, successful lasing action was obtained under room-temperature (RT) CW conditions by photopumping with a low threshold pump intensity and a lasing wavelength of 1.22 /spl mu/m.