The type-II band alignment of particular III/V heterostructures is a promising route towards achieving certain wavelengths on specific substrates, which would not be possible with type-I structures. One example is telecommunication lasers on GaAs substrates. This study reports on the progress in combining dilute nitrides and dilute bismides in W-type hetero structures to improve the luminescence intensity, which is a fundamental prerequisite for future incorporation in a laser structure. Increasing the emission wavelength of these structures is challenging and the interface formation is critical, especially as two metastable materials are combined. Here, we investigate the impact of different interface configurations by growing Ga(N,As)/Ga(As,Bi) and Ga(As,Bi)/Ga(N, As) type-II structures. We employ metal-organic vapor phase epitaxy (MOVPE) to grow Ga(N,As) and Ga(As,Bi) layers and investigate the effects of interlayer thicknesses on the structural and optical properties of the hetero structures. The results indicate that - while the introduction of a GaAs interlayer can affect the direct and indirect transitions intensities - it does not significantly improve the interface quality. However, this is strongly influenced by the order in which the materials are grown. The growth of Ga(N,As) on Ga(As,Bi) shows no peculiarities, while the type II transition energy is shifted to lower energies when Ga(As,Bi) is grown on Ga(N,As). High-resolution X-ray diffraction (HR-XRD), photoluminescence (PL) spectroscopy, atomic force microscopy (AFM), and scanning transmission electron microscopy (STEM) were used to characterize the samples.

Tuning the bandgap in ternary III-V semiconductors via modification of the composition or the strain in the material is a major approach for the design of optoelectronic materials. Experimental approaches screening a large range of possible target structures are hampered by the tremendous effort to optimize the material synthesis for every target structure. We present an approach based on density functional theory efficiently capable of providing the bandgap as a function of composition and strain. Using a specific density functional designed for accurate bandgap computation (TB09) together with a band unfolding procedure and special quasirandom structures, we develop a computational protocol efficiently able to predict bandgaps. The approach's accuracy is validated by comparison to selected experimental data. We thus map the phase space of composition and strain (we call this the ``bandgap phase diagram'') for several important III-V compound semiconductors: GaAsP, GaAsN, GaPSb, GaAsSb, GaPBi, and GaAsBi. We show the application of these diagrams for identifying the most promising materials for device design. Furthermore, our computational protocol can easily be generalized to explore the vast chemical space of III-V materials with all other possible combinations of III- and V-elements.

We investigate the temperature-dependence of modal gain for type-II (GaIn)As/Ga(AsSb) “W”-laser structures operating around the O-band. Measurements show their potential to control the temperature dependence of the gain due to carrier-induced band bending effects. This is of interest to semiconductor laser and optical amplifier applications.

Abstract The ongoing pursuit for laser device emitting in the near‐infrared spectral region on GaAs substrates has led to various material systems and device concepts. Alloys containing dilute amounts of Bismuth are promising candidates due to the already substantial band gap shift when incorporating low molar fractions of Bi in the GaAs host lattice. However, devices emitting at technologically essential wavelengths of 1.3 and 1.55 μm have yet to be demonstrated using this material system. Especially the non‐equilibrium nature of the growth conditions required to grow the metastable material makes epitaxial growth with high molar fractions of Bi challenging. An alternate approach to reach the desired wavelengths exploits a type‐II band alignment between two materials to push the emission wavelength further into the telecom bands. Here, room‐temperature laser operation of the first type‐II structure employing Ga(As,Bi) as hole confining layer and (Ga,In)As as electron confining layer is demonstrated. Sample growth is conducted by low‐pressure metalorganic vapour phase epitaxy. Broad area laser devices are processed and characterized by electroluminescence measurements. A threshold current density of 3.86 kA/cm2 and emission wavelength of 1037 nm are observed, showing this device concept's potential for future lasers in the telecom bands.

Energy efficiency, superior performance, and long-term reliability are crucial advantages of GaAs-based semiconductor laser diodes featuring strained type-I quantum wells as active regions. This class of semiconductor structures provides very good performance in the near-infrared spectral range. Achieving longer wavelength emission on GaAs substrates has proven to be difficult so far. Alloys including nitrogen (N) and bismuth (Bi) promise active materials with the possibility to push this accessible emission wavelength range toward the telecommunication bands. The alloys show a drastic decrease in the band-gap energies already for small fractions of the respective elements. However, the strong nonequilibrium nature of such multinary alloys has rendered sufficient incorporation with reasonable material quality impossible so far, mandating alternate approaches. Here, we embed a Ga(As,Bi) quantum well (QW) between two Ga(N,As) QWs in a so-called W-type quantum well heterostructure (WQW). This approach has the potential to achieve significant optical gain due to sufficient wave-function overlap, which is enhanced compared to type-II heterostructures. In particular, we realize WQWs with emission wavelengths around 1.1, 1.3, and 1.4 mu m by drastically altering the growth conditions compared to standard growth conditions established for type-I QW structures. This particularly applies to Bi segregated at the interfaces in the structure. The resulting recipes enable the future growth of tailored WQWs for even longer emission wavelengths, e.g., extending beyond the telecom bands into the fingerprint region in the midinfrared.

The realization of efficient semiconductor lasers on GaAs substrates operating at 1.55 μm and beyond remains a technological challenge. As a potential solution, epitaxial heterostructures with type-II band alignment are currently discussed as an active region. Each individual layer in such heterostructures features a comparably large bandgap energy; therefore, spurious effects in laser operation such as reabsorption, multi-photon absorption, or Auger scattering are expected to be suppressed. The actual laser operation occurs across the internal interfaces as the electron and hole wave functions have their extrema in adjacent layers. Hence, a large wave-function overlap is key for efficient recombination. A direct comparison of symmetric and asymmetric Ga(N,As)/Ga(As,Bi) type-II quantum well heterostructures reveals that the symmetry of the layer arrangement drastically influences the charge-carrier recombination: disorder in the Ga(As,Bi) layer has more prominent effects for the asymmetric configuration compared to the symmetric one. The temperature dependence of the emission energy is mainly influenced by the Ga(N,As)-electron layers, while the temperature dependence of the full width at half maximum and the excitation dependence of the emission energy are dominated by the Ga(As,Bi)-hole layers. Photoluminescence excitation spectroscopy reveals the corresponding carrier-relaxation paths to the type-II transition.

We discuss a new class of type-II quantum wells (QWs) that exploit the impact of Bi and N on the GaAs band-structure. Via growth, experiment, and theoretical calculations we highlight the properties of GaAs1xBix/GaNyAs1-y "W" QWs, demonstrating a potential pathway to uncooled telecom-wavelength laser operation.

Tertiarybutylarsine (TBAs) and tertiarybutylphosphine (TBP) are getting more and more established as group V precursors for the growth of V/III semiconductors by metal organic vapor phase epitaxy (MOVPE). Due to this development, the thermal decomposition of these precursors was studied during the growth of GaAs and GaP utilizing the Ga precursors, trimethylgallium (TMGa), triethylgallium (TEGa), and tritertiarybutylgallium (TTBGa), in a horizontal AIXTRON AIX 200 GFR MOVPE system. The decomposition and reaction products were measured in line with a real-time Fourier transform quadrupole ion trap mass spectrometer from Carl Zeiss SMT GmbH. The decomposition temperatures and the related activation energies were determined for all the mentioned precursors under comparable reactor conditions. The decomposition curves suggest, on the one hand, a catalytic effect of the GaAs surface on the decomposition of TBAs. On the other hand, the decomposition products indicate alkyl exchange as a relevant step during the bimolecular decomposition of TBAs and TBP with the Ga precursors TMGa, TEGa, and TTBGa. The catalytic reaction reduces the decomposition temperature of TBAs and TBP by up to 200 °C. In addition, for the growth of GaAs with TBAs and TEGa and for the growth of GaP with TBP and TEGa, a significant decrease of the decomposition temperature with an increasing V/III ratio is observed. This behavior, which is related to an alkyl exchange reaction, gives insights into the low-temperature growth of GaAs and GaP and is converted into an effective V/III ratio. Finally, the growth of GaAs with TTBGa and TBAs is realized at 300 °C below the unimolecular decomposition temperature of TBAs, underlining the catalytic effect of the GaAs surface. Altering the growth surface with trimethylbismuth led to the prevention of the catalytic effect.

III/V semiconductors containing small amounts of nitrogen (dilute nitrides) are promising for applications such as lasers and solar cells. Metal-organic vapor-phase epitaxy (MOVPE) is a widely used technique for growing III/V semiconductors on an industrial scale, and the growth of dilute nitrides with this method is promising for later successful market entry. The main issues of dilute nitrides are carbon incorporation and low nitrogen incorporation efficiency of the conventional N precursors. Due to the high N incorporation efficiency and the low decomposition temperature of the As and N precursor di-tert-butylaminoarsane (DTBAA), a similar P- and N-containing precursor, di-tert-butylaminophosphane (DTBAP), was synthesized and purified on a laboratory scale. Growth studies using this precursor were carried out in this work realizing Ga(N,P)/GaP multi quantum wells on Si and GaP substrates. The structures show evidence of N incorporation, and good layer structures were confirmed by high-resolution X-ray diffraction. Following the influence of different growth parameters on the N incorporation, the growth rate and surface morphology were characterized to set a foundation for possible growth applications in the future. DTBAP shows many advantages over the conventional N source 1,1-dimethylhydrazine (UDMHy) such as a much lower decomposition temperature of 310 degrees C and the realization of Ga(N,P) layers grown at temperatures as low as 475 degrees C with a high N incorporation of over 10%. Furthermore, the gas-phase decomposition of DTBAP has been studied with a real-time fast Fourier transform quadrupole ion trap mass spectrometer attached inline to the MOVPE reactor. The decomposition of DTBAP behaves very similarly to the As analogue DTBAA. On the one hand, the tert-butyl groups attached to DTBAP decompose radically, leading to the formation of isobutane, and decompose, on the other hand, by beta-H elimination, leading to the formation of isobutene. Furthermore, the decomposition products indicate a direct cleavage of the P-N bond of the molecule, resulting in the formation of aminyl radicals (NH2 center dot). The formation of NH2 center dot explains the high N incorporation efficiency of DTBAP at low temperatures as well as its limitations due to loss of NH3 at higher temperatures.

III/V semiconductors containing bismuth (Bi) show some interesting properties for high efficient optoelectronic applications in the near- and mid-IR region. However, the alloys are highly metastable due to the large covalent radius of the Bi atom compared to the other group V atoms, which are replaced in the cubic zinc-blende lattice. Hence, carefully adjusted growth conditions at low growth temperatures are required in order to incorporate a significant amount of Bi into the host lattice. In this book chapter, we review our current understanding of the growth of dilute Bi-containing III/V semiconductor alloys on GaAs substrates, the factors, which limit the Bi incorporation, as well as the application of the material in electrically pumped LASER diodes. Bi fractions of up to 4.2% Bi and 7% Bi can be achieved using metal-organic vapor phase epitaxy (MOVPE) as growth technique using pulsed as well as continuous flow conditions, respectively. The influence of different growth conditions, i.e., the growth temperature and partial pressures of the used precursors are investigated and the results are discussed in detail. Exceeding a critical Bi concentration, accumulation of metal droplets on the surfaces is found which hampers high-quality growth of subsequent layers, which is however necessary for devices. This limitation in the Bi incorporation makes quaternary alloys, like GayIn1−yAs1−xBix structures on GaAs substrates interesting for optoelectronic applications. Optimization of the material quality resulted in the demonstration of electrically pumped GaAs1−xBix laser diodes with up to 4.1% Bi operating at room temperature. As there is this current upper limit of 7% Bi incorporation using MOVPE growth, we discuss factors, which might influence and limit the Bi incorporation in the host material. The use of alternative Bi precursors is investigated with regard to the impact of different carbon (C)-containing radicals on the surface. The impact of strain on the Bi incorporation is discussed by adding nitrogen or phosphorus and hence tensilely prestraining the layer. Finally, we also investigate the influence of trimethylindium (TMIn) on the Bi incorporation in GayIn1−yAs1−xBix and compare its growth to the one of GaAs1−xBix.

The incorporation of dilute amounts of Bi into the host lattice of a III/V semiconductor has a strong influence on its electronic properties. The bandgap is strongly redshifted which makes these materials interesting for application in the near- to mid-infrared regime. Furthermore, the spin-orbit splitting is increased resulting in suppression of hot-hole producing Auger recombination, which makes the fabrication of highly efficient optical devices feasible. However, for ternary Ga(As,Bi) grown using metalorganic vapor phase epitaxy (MOVPE), it has proven difficult to achieve the desired composition of the ternary material. Therefore, the additional incorporation of indium (In) into Ga(As,Bi), which should induce a further redshift of the bandgap, is investigated and summarized in this paper. For deposition of quaternary (Ga,In)(As,Bi), two different low temperature growth techniques using MOVPE are conducted. The strain and photoluminescence peak positions of the samples are correlated to estimate the composition of the (Ga,In)(As,Bi) layers. It was found that the trimethylindium and tertiarybutylarsine supplies need to be carefully adjusted to grow high quality bulk materials and that the incorporation of indium is inversely related to the amount of incorporated Bi.

III–V semiconductors containing small amounts of nitrogen (“dilute nitrides”) are very promising material systems for optoelectronic applications. Devices based on dilute nitrides currently suffer from problematic C incorporation. To overcome this problem, a novel nitrogen (N) and arsenic (As) precursor for metal–organic vapor phase epitaxy (MOVPE) of the dilute nitride di-tert-butylaminoarsane (DTBAA) has been introduced. DTBAA in comparison to the commonly used 1,1-dimethylhydrazine (UDMHy) showed a significantly improved N incorporation efficiency. The molecule exhibits no strong carbon (C)–N bond, and the C is only present in large alkyl groups which form fewer C radicals since β-H elimination is the dominating decomposition process. This should significantly lower the problematic C incorporation in dilute nitrides and lead to highly efficient devices. To understand the high N incorporation efficiency as well as the As incorporation, the gas-phase decomposition of this novel precursor has been studied with a real time Fourier transform (FT) quadrupole ion trap mass spectrometer (iTrap) from Carl Zeiss SMT GmbH in a horizontal Aixtron Aix 200 GFR MOVPE reactor. Formation of isobutane and isobutene proves a radical cleavage and β-H-elimination as decomposition processes of the tert-butyl groups attached to the molecule. Furthermore, the appearance of ammonia (NH3) has been detected. This indicates a direct cleavage of the As–N bond of the molecule, resulting in the formation of an aminyl radical (NH2•). The formation of NH2• explains the high N incorporation efficiency of DTBAA as well as its limitations due to desorption of NH3 at higher temperatures.

The incorporation of small fractions of bismuth atoms in III–V semiconductors such as (Ga,In)As leads to a vast decrease of the bandgap energies accompanied by an increase of the spin-orbit splitting energies of the alloy compared to the host material. This effect is commonly described by an anticrossing of the bismuth-level with the valence bands of the matrix. Growth and characterization of quaternary alloys like (Ga,In)(As,Bi) remains challenging due to the required low growth temperatures, since Bi generally tends to have pronounced surfactant properties on the one hand and the similar influence in Bi and In on most structural, electronic, and optical properties such as the lattice constant or the bandgap energy. In this study, we uniquely identify surface diffusion of the bismuth atoms with X-ray photoelectron spectroscopy and relate the finding to growth parameters and photoluminescence properties and X-ray diffraction patterns of the material. We show the influence of different partial pressures of the MOVPE growth on the bismuth segregation process as well as a consequence thereof the disorder properties of those samples compared to (Ga,In)As/InP reference alloys.