Shiro Miwa

Effects of interfacial chemistry on the formation of interfacial layers and faulted defects in ZnSe/GaAs

Existence of Zn‐As and Ga‐Se interfacial layers were suggested by transmission electron microscopy in Zn treated and Se treated or reacted ZnSe/GaAs interfaces, respectively. High densities of As precipitates and Shockley partials were introduced in films with Zn treatment on a c(4×4) As‐rich GaAs surface. In addition, high densities of vacancies and Shockley partials were obtained in samples with a Se‐reacted ZnSe/GaAs interface. Formation of the Shockley partials may originate from the stacking errors induced by disordering of Zn‐ or Ga‐interstitials on the GaAs surface.

DEPENDENCE OF GENERATION AND STRUCTURES OF STACKING FAULTS ON GROWING SURFACE STOICHIOMETRIES IN ZNSE/GAAS

Thin ZnSe films were grown by molecular beam epitaxy on Zn exposed (2×4) As‐stabilized surfaces of GaAs epilayers under varied beam flux ratios. A very low density of faulted defects in the range of ∼ 104/cm2 was generated in samples grown under a condition with a mixture of both (2×1) and weak c(2×2) surface reconstructions at the initial stages of growth. However, an asymmetric distribution on the densities of extrinsic cation‐ and anion‐terminated Shockley‐type stacking faults were generated, respectively, in samples grown under Zn‐ and Se‐rich surface stoichiometries.

Nature and origins of stacking faults from a ZnSe/GaAs interface

Existence of ∼3–4 monolayers of Ga2Se3- and Ga2Te3-like interfacial layers are suggested by transmission electron microscopy of Se- and Te-exposed (or -reacted) ZnSe/GaAs interfaces, respectively. Densities of extrinsic Shockley- and intrinsic Frank-type stacking faults are of ∼5 ×107/cm2 in samples grown on Se- or Te-exposed GaAs surfaces. Annealing on the Se- or Te-exposed GaAs generated a high density of vacancy loops (⩾1×109/cm2) with an increase of the densities of both intrinsic and extrinsic-type stacking faults (⩾5×108/cm2) after growth of the films. Formation of the intrinsic stacking faults or vacancy loops and extrinsic stacking faults may be related to the presence of cation vacancies and interstitials, respectively, on the surface of the GaAs epilayer, due to the interaction between Se or Te and the GaAs epilayer with charge unbalanced Ga–Se or Ga–Te bondings. On the other hand, ∼2 and 3–4 monolayers of Zn–As interfacial layers are recognized in samples grown on Zn-exposed GaAs-(2×4) and -c(4...

Origin of n‐type conduction at the interface between epitaxial‐grown layer and InP substrate and its suppression by heating in phosphine atmosphere

The origin of unintentionally introduced n‐type conduction at the interface of epitaxially grown layer‐InP substrate is identified. From the relation between the sheet carrier concentration and the etching depth, an n‐type conducting layer was found at the epitaxial layer‐substrate interface. The sheet carrier concentration and the sheet Si concentration at the surface of the InP substrate, which was obtained by secondary ion mass spectrometry analysis, agreed well. As a result, we determined that the Si atoms caused n‐type conduction. To make clear that origin of the Si atoms, the following possibilities were investigated. One possibility was the vessel made from silicon dioxide (SiO2), which was used for etching the substrates, but it was determined not to be the cause because no significant difference was observed between a teflon or polypropylene vessel. To investigate the contamination from the air, we used metalorganic chemical vapor deposition to prepare a sample composed of a InP capping layer reg...

The role of zinc pre-exposure in low-defect ZnSe growth on As-stabilized GaAs (001)

Zinc coverage and the structures of Zn-exposed As-stabilized GaAs(001)-(2×4) and -c(4×4) surfaces have been studied using x-ray photoelectron spectroscopy and scanning tunneling microscopy in order to clarify the role of the Zn pre-exposure process in ZnSe growth on GaAs(001). Since Zn atoms stick on the GaAs-(2×4) surface even though their interaction is very weak, Zn may act as a balancer to form a neutral ZnSe/GaAs interface. Zn can also remove excess As atoms and make a “pure” (2×4) structure that is the only possible starting surface for low-defect ZnSe heteroexpitaxy on a GaAs(001) surface.

In situ characterization of ZnSe/GaAs(100) interfaces by reflectance difference spectroscopy

We discuss the structure and formation mechanism of ZnSe/GaAs(100) interfaces as probed by reflectance difference spectroscopy (RDS). First we describe a simple analytic procedure that separates the surface and interface contributions in the RD spectra obtained for a heterostructure. The procedure opens up the new possibilities of RDS as an in situ interface probe. We have applied this technique to characterize the ZnSe/GaAs interfaces prepared on various GaAs(100) surfaces. The interface‐anisotropy spectra thus obtained and the cross‐sectional transmission electron microscopy, show clearly that the chemical composition of the interfacial layer can be changed by controlling the reconstruction and the pregrowth Zn and Se treatments of the initial GaAs surface.

The effects of oxygen on the electronic and optical properties of AlInAs layers lattice‐matched to InP substrates grown by atmospheric‐pressure metal‐organic chemical vapor deposition

AlInAs layers lattice‐matched to InP substrates were grown by atmospheric‐pressure metal‐organic chemical vapor deposition. The residual oxygen concentration determined by secondary ion mass spectrometry ranged from 3×1016 to 3×1019 cm−3, and was high when the growth temperature was low or the V/III ratio was low. The oxygen concentration and the residual carrier concentration showed the same dependence on the V/III ratio in the high V/III ratio region. This suggests that oxygen is the origin of the residual carrier concentration. Strong correlations between the oxygen concentration and the photoluminescence intensity and reverse current through Schottky diodes suggest that oxygen creates generation‐recombination centers in AlInAs layers.

Characterization and control of II-VI/III-V heterovalent interfaces

Abstract We have systematically studied the structure, chemical composition, and formation processes of ZnSe/GaAs(0 0 1) interfaces where heterovalency plays an important role. Prior to ZnSe growth, the initial surfaces were prepared by exposing differently reconstructed GaAs surfaces to a beam ofZn, Se, or Te. It has been shown that the structure and the composition of this interface can be well controlled by the preparation procedures of initial GaAs surfaces. We have also found that generation of the faulted defects in ZnSe films is closely related with the formation of interface layers.

Non-contact and non-destructive measurement of carrier concentration of nitrogen-doped ZnSe by reflectance difference spectroscopy

We report an optical technique to determine the net carrier concentration of nitrogen-doped ZnSe, N a-N d. An optical anisotropy induced by the built-in field was measured by reflectance difference spectroscopy (RDS). It has been shown that the energy derivative of the RD signal near 5 eV is proportional to (N a-N d)1/3 when N a-N d>5×1016 cm-3. The physical origin of the observed power law is discussed. We also address the origin of the surface roughness induced baseline in the RD spectra which affects the accuracy of the measurement.

Self-assembled formation of ZnCdSe quantum dots on atomically smooth ZnSe surfaces on GaAs(001) by molecular beam epitaxy

Abstract We investigate growth conditions to obtain atomically flat ZnSe film surfaces on GaAs(001) without forming ZnSe-related dot structures. It is found that high temperature growth is favorable for the growth of ZnSe with a smooth surface. In order to prevent degradation of interface properties at high substrate temperature, two-step growth of ZnSe layers is employed, where a low-temperature growth step is followed by high temperature growth. The two-step process enables one to grow ZnSe with atomically flat surface without ZnSe-related dots structures. The formation of self-assembled ZnCdSe quantum dots (QDs) is achieved on such atomically surfaces. Typical QD size is: base diameter of 21±3 nm and height of 8±2 nm. Even at a total deposition of ZnCdSe of 3.5 monolayer (ML), the QD density is as low as ∼2.4 μm −2 . It is found that these QDs are formed on a ZnCdSe wetting layer whose thickness is at least 3 ML.