K. C. Rajkumar

Onset of incoherency and defect introduction in the initial stages of molecular beam epitaxical growth of highly strained InxGa1−xAs on GaAs(100)

Direct evidence for interplanar relaxation in islands at the initial stages of strained epitaxy is presented using molecular beam epitaxically deposited In0.5Ga0.5As on GaAs(100). Concomitant existence of atomic displacements in the substrates to unexpectedly large depths of ∼150 A is found. In incoherent islands, defects are found to be introduced symmetrically near the island edges.

Growth control of GaAs epilayers with specular surface free of pyramids and twins on nonmisoriented (111)B substrates

Growth control of GaAs epilayers with specular surface, free of superficial pyramid‐shape features and bulk twins, is achieved on a nonmisoriented GaAs(111)B substrate via in situ, real time measurement of specular beam intensity of reflection high‐energy electron diffraction (RHEED). Regimes of growth conditions are identified in terms of the static surface phase diagram and the temporal RHEED intensity behavior during growth, thus affording the possibility to realize a reproducible control independent of growth systems.

In situ approach to realization of three‐dimensionally confined structures via substrate encoded size reducing epitaxy on nonplanar patterned substrates

We report the first realization of three‐dimensionally confined semiconductor heterostructures via a one‐step growth on nonplanar patterned substrate. Truncated pyramidal shaped mesas on GaAs (111)B patterned substrates are employed and a substrate encoded size reducing epitaxical growth process exploited to realize GaAs pinched‐off pyramidal volumes of base ∼50 nm and height 13 nm.

Optically active three-dimensionally confined structures realized via molecular beam epitaxical growth on nonplanar GaAs (111)B

We report the first realization on nonplanar patterned substrates of optically active three‐dimensionally confined semiconductor volumes created in situ via a one‐step molecular beam epitaxial growth. Growth is carried out on pyramidal mesas on (111)B substrates and in a regime that results in the emergence of three equivalent {110} side facets which overtake the as‐patterned {100} side facets and lead to mesa pinch‐off. Transmission electron microscopy along with spatially and spectrally resolved cathodoluminescence provide evidence for emission from laterally confined regions with lateral linear dimensions ≲100 nm.

Realization and analysis of GaAs/AlAs/In0.1Ga0.9As based resonant tunneling diodes with high peak-to-valley ratios at room temperature

Investigations of pseudomorphic resonant tunneling diodes based on the GaAs/AlAs/In0.1Ga0.9As material system reveal that the use of undoped In0.1Ga0.9As spacer layers gives rise to a significantly enhanced peak‐to‐valley ratio of 3.2 and 14 at 300 and 77 K, respectively, as opposed to 2 and 5 obtained with the use of conventional GaAs spacers in an otherwise identical structure. This is achieved without any significant degradation of the peak current density but rather through reduction of the undesired nonresonant valley current. Comparison of the experimental results with calculations done using the Airy function transfer matrix approach indicates that the Γ‐X discontinuity at the GaAs/AlAs and In0.1Ga0.9 As/AlAs interface is relevant for electron tunneling, along with the smaller transverse effective mass of 0.19m0 in the AlAs X valley. We also find that In0.1Ga0.9As layers grown under an excess As‐stabilized growth condition give better results than those grown under a barely As‐stabilized condition.

Optical absorption and modulation behavior of strained InxGa1−xAs/GaAs(100)(x≤0.25) multiple quantum well structures grown via molecular beam epitaxy

We report on the optical absorption and modulation characteristics of strained InxGa1−xAs/GaAs(0.1≤x≤0.25) multiple quantum well (MQW) structures grown on GaAs (100) substrates which also included regions of prepatterned mesas. Sharp excitonic features were realized in samples optimally grown by employing reflection high‐energy electron diffraction. High optical quality MQW structures as thick as 1.5 μm are realized. To date, the highest modulation per unit field at low fields (<50 kV/cm) in this system is achieved.

Relation between reflection high‐energy electron diffraction specular beam intensity and the surface atomic structure/surface morphology of GaAs(111)B

The intensity behavior of the specular beam in reflection high‐energy electron diffraction (RHEED) from GaAs(111)B grown by molecular‐beam epitaxy (MBE) is investigated for various growth and diffraction conditions. The temporal behavior during the initial growth of a buffer layer is examined at a fixed diffraction condition. Intensity increase is observed during and after the initial stages of buffer layer growth and found to saturate after about 80 monolayer growth. Intensity oscillations are seen starting at different moments of initial growth, the earliest observed after only 14 monolayer growth. These results are used to guide and control GaAs(111)B growths with mirrorlike surface morphology.

Realization of low defect density, ultrathick, strained InGaAs/GaAs multiple quantum well structures via growth on patterned GaAs (100) substrates

Growth of low defect density highly strained InxGa1−xAs/GaAs multiple quantum well (MQW) structures of thicknesses suited for application in spatial light modulator (SLM) devices operating in infrared has been thwarted by the occurrence of strain‐induced defects. Exploiting the notion of strain relief at mesa edges, we report here the first realization of very low defect density MQW structures of thickness as high as 2.38 μm at x=0.20. This has opened up the possibility of realizing a variety of reflective and transmissive SLM structures which also fruitfully exploit the transparent nature of the substrate.

Realization of three‐dimensionally confined structures via one‐step in situ molecular beam epitaxy on appropriately patterned GaAs(111)B and GaAs(001)

The realization of three‐dimensionally confined GaAs/AlGaAs structures on GaAs (111)B and GaAs (001) substrates via one step in situ molecular beam epitaxy is reported. Growth is carried out on nonplanar patterned substrates with crystallographically equivalent mesa top edges. Equivalent side facets evolve during growth and completely surround the mesa top. Adatom migration from these facets to the mesa top result in shrinkage of the mesa top area leading to mesa pinch‐off. Scanning and transmission electron microscopy provide evidence for the realization of structures with lateral linear dimensions ≲500 A. Cathodoluminescence images from the (111)B structures attest to their high optical quality.

High contrast ratio asymmetric Fabry–Perot reflection light modulator based on GaAs/InGaAs multiple quantum wells

We report the realization of both high contrast ratio (66:1) and dynamic range (30%) at room temperature in a strained GaAs/InGaAs(100) multiple quantum well based asymmetric Fabry–Perot reflection modulator. The p‐i‐n configuration modulator also acts as a photodetector and exhibits a high quantum efficiency (∼80%).