Yoshito Nishijima

PbSnTe multiple quantum well lasers for pulsed operation at 6 μm up to 204 K

Lattice‐matched PbSnTe‐PbTeSe multiple quantum well lasers fabricated by hot wall epitaxy have been developed. Though the PbSnTe‐PbTeSe system is a type I’ superlattice, by using band bending due to doping, laser operation like type I superlattices has been achieved for the first time. The laser worked well in pulsed operation up to 204 K with 6 μm radiation (cw operation at 130 K with 6.6 μm radiation).

Direct growth of CdTe on (100), (211), and (111) Si by metalorganic chemical vapor deposition

CdTe epilayers were grown directly on (100), (211), and (111) silicon substrates by metalorganic chemical vapor deposition (MOCVD). The crystallinity and the growth orientation of the CdTe film were dependent on the surface treatment of the Si substrate. The surface treatment consisted of exposure of the Si surface to diethyltelluride (DETe) at temperatures over 600°C prior to CdTe growth. Direct growth of CdTe on (100) Si produced polycrystalline films whereas (lll)B single crystals grew when Si was exposed to DETe prior to CdTe growth. On (211) Si, single crystal films with (133)A orientation was obtained when grown directly; but produced films with (211)A orientation when the Si surface was exposed to DETe. On the other hand, only (lll)A CdTe films were possible on (111) Si, both with and without Te source exposure, although twinning was increased after exposure. The results indicate that the exposure to a Te-source changes the initial growth stage significantly, except for the growth on (111) Si. We propose a model in which a Te atom replaces a Si atom that is bound to two Si atoms.

111)A CdTe rotation growth on (111) Si with low growth rate by metalorganic chemical vapor deposition

(111)A CdTe epilayers have been grown directly on (111) silicon substrates with the low growth rate of less than 0.5 μm/h by metalorganic chemical vapor deposition (MOCVD). The full width at half maximum (FWHM) of the x‐ray rocking curve of a 1 μm thick epilayer is 100 arcsec, which is much better than the value for (111)B CdTe/(100)Si. The low growth rate effects are deduced from the classical capillarity theory. The nucleation stages were examined by atomic force microscopy (AFM), which showed that the nuclei were less in number when growing with the low growth rate. The geometrical advantages of (111)A CdTe/(111) Si for annihilating the dislocations are also discussed.

Polarity of a (111)‐oriented CdTe layer grown on a (100) Si substrate

Direct epitaxial growth on silicon has advantages when fabricating monolithic integrated infrared focal‐plane arrays. We demonstrated that both (111)A and (111)B oriented CdTe layers can be grown on (100) Si substrates by molecular‐beam epitaxy. The surface morphology of the (111)A layer was rough, while that of the (111)B layer was smooth. The key determining polarity is the substrate temperature during preadsorption of Te2 flux. We found a polarity transition at 450 to 500 °C, and (111)B layers grow above that temperature.

1.3 µm InGaAs/InAlGaAs Strained Quantum Well Lasers on InGaAs Ternary Substrates

InGaAs/InAlGaAs strained quantum well lasers with 1.3 µm wavelength have been realized on In0.31Ga0.69As ternary substrates for the first time, owing to the increased indium composition of the substrates. A temperature-insensitive slope efficiency of -0.007 dB/K has been observed. The threshold current density (Jth) at 20°C and characteristic temperature (T0) are 677 A/cm2 and 76 K, respectively. The dependence of T0 on Jth per well suggests that higher T0 would be achieved by fabricating the lasers on InGaAs substrates of improved quality, thereby decreasing Jth.

Growth of (111) HgCdTe on (100) Si by MOVPE using metalorganic tellurium adsorption and annealing

Abstract(lll)B CdTe layers free of antiphase domains and twins were directly grown on (100) Si 4°-misoriented toward<011> substrates, using a metalorganic tellurium (Te) adsorption and annealing technique. Direct growth of (lll)B CdTe on (100) Si has three major problems: the etching of Si by Te, antiphase domains, and twinning. Te adsorption at low temperature avoids the etching effect and annealing at a high temperature grows single domain CdTe layers. Te atoms on the Si surface are arranged in two stable positions, depending on annealing temperatures. We evaluated the characteristics of (lll)B CdTe and (lll)B HgCdTe layers. The full width at half maximum (FWHM) of the x-ray double crystal rocking curve (DCRC) showed 146 arc sec at the 8 |im thick CdTe layers. In Hg1−xCdxJe (x = 0.22 to 0.24) layers, the FWHMs of the DCRCs were 127 arc sec for a 7 (im thick layer and 119 arc sec for a 17 (im thick layer. The etch pit densities of the HgCdTe were 2.3 x 106 cm2 at 7 ^m and 1.5 x 106 cm-2 at 17 um.

VIII ratio dependence of surface macrodefects in CdTe/ZnTe/GaAs(100) growth by metalorganic vapor phase epitaxy

We studied the surface morphology of CdTe(100) layers on GaAs(100) by metalorganic vapor phase epitaxy (MOVPE). When CdTe(100) layers were obtained using thin ZnTe nucleation layers, we observed high-density pyramidal macrodefects, known as hillocks, in the epilayer surface. We found the density of hillocks to be strongly dependent on the VIII ratio during both ZnTe and CdTe growth processes. We optimized both the TeZn and TeCd ratios to obtain a minimum hillock density of 1 × 102 cm−2. These results show that hillocks were nucleated at both the epilayer/substrate and CdTeZnTe interfaces. By X-ray diffraction measurement, we confirmed that the quality of the crystal structural was also good under this condition. We also found the initial nucleation conditions to be more important for the structural quality. In (100)HgCdTe/CdTe/GaAs growth, pyramidal hillocks on the CdTe buffer surface caused substantial (> 100 μm) macrodefects in HgCdTe layers, which were fatal for infrared devices. Their shape was enlarged especially in one direction. To achieve a low density of surface macrodefects in HgCdTe(100) or CdTe(100) layers on GaAs(100) substrates, we need to precisely control the VIII ratio.

Dislocation profiles in HgCdTe(100) on GaAs(100) grown by metalorganic chemical vapor deposition

We studied dislocation etch pit density (EPD) profiles in HgCdTe(lOO) layers grown on GaAs(lOO) by metalorganic chemical vapor deposition. Dislocation profiles in HgCdTe(lll)B and HgCdTe(lOO) layers differ as follows: Misfit dislocations in HgCdTe(lll)B layers are concentrated near the HgCdTe/CdTe interfaces because of slip planes parallel to the interfaces. Away from the HgCdTe/CdTe interface, the HgCdTe(111)B dislocation density remains almost constant. In HgCdTe(lOO) layers, however, the dislocations propagate monotonically to the surface and the dislocation density decreases gradually as dislocations are incorporated with increasing HgCdTe(lOO) layer thicknesses. The dislocation reduction was small in HgCdTe(lOO) layers more than 10 μm from the HgCdTe/CdTe interface. The CdTe(lOO) buffer thickness and dislocation density were similarly related. Since dislocations glide to accommodate the lattice distortion and this movement increases the probability of dislocation incorporation, incorporation proceeds in limited regions from each interface where the lattice distortion and strain are sufficient. We obtained the minimum EPD in HgCdTe(100) of 1 to 3 x 106 cm-2 by growing both the epitaxial layers more than 8 μm thick.

PbSnTe double‐heterostructure lasers and PbEuTe double‐heterostructure lasers by hot‐wall epitaxy

Pb1−x Snx Te, double‐heterostructure (DH) lasers and Pb1−x Eux Te DH lasers produced by hot‐wall epitaxy have been studied. The growth temperature for both laser crystals is 300 °C. This is lower than the growth temperatures obtainable by molecular‐beam epitaxy and liquid phase epitaxy. By investigating the I‐V characteristics of Pb1−x Snx Te DH lasers with x values greater than 0.2, it was confirmed that the band structure of the p‐n heterojunction is type 1’. A Pb1−x Snx Te1−y Sey layer, rather than a PbTe1−y Sey layer, should be used for the cladding layer of Pb1−x Snx Te DH lasers with x values greater than 0.2. One of the primary factors preventing an increase in the maximum operating temperature to 200 K is that the carrier density injected into the active layer is not sufficient for laser emissions over 200 K due to the p‐n heterojunction of the type 1’ band structure. The band structure of the p‐n heterojunction of Pb1−x Eux Te DH lasers is type 1. Therefore, the maximum operating temperatures of ...

CdTe(111)B/Si(100) structure grown by metalorganic vapor phase epitaxy with Te adsorption and annealing

We studied the crystal structure of CdTe(111)B layers directly grown on Si(100) by MOVPE using a new pre-growth process, which includes a metalorganic Te adsorption and an annealing process. In this paper, we discussed the CdTe structure from the three aspects of antiphase, twinning and tilt. We investigated the dependence of the antiphase content in CdTe(111)B on the anneal temperature and the Si misorientation angle. From the results, we assume that the origin of the antiphase formation is the difference in the arrangement of adsorbed Te atoms. Te arrangement leading to antiphase formation occurs on Si terraces away from steps at relatively low temperatures. We reduced most of the twinning in epilayers by optimizing the VI/II ratio. We think the remaining twinning was confined to near the interface and it nucleated from the Te arrangement on terraces. We found that the Si(100)-CdTe(111) tilt was much smaller than that expected from the well-known Nagai model. We propose that a negative tilt is induced to reduce the lateral mismatch. To adjust the lateral distance of unit cells, 30 CdTe lattices match to 31 Si lattices. CdTe(111)B planes are inclined to reduce the remaining mismatch between two lattices. This initial tilt also causes wider CdTe terraces. We modified Nagais tilting model for this reconstructed CdTe surface. The total tilt angle is defined by these two tilting mechanisms.