Hiroyuki Kasano

Cathodoluminescence of Ca1 − x Mg x S : A ( A = Eu or Ce )

Cathodoluminescent properties of Eu/sup 2 +/ - or Ce/sup 3 +/ -activated MgS and Ca/sub 1//sub -/..integral.. Mg..integral..S phosphors are investigated at 300 K. It found that MgS:Eu(0.01 mole percent (m/o) exhibits a high energy efficiency (about 16%) and a improved waterresistance if residual oxide content is less than 1 m/o. Under these highly sulfurizing conditions MgS is confirmed to be completely miscible with CaS in any compositional ratio. The composition Ca /sub 0.1/ Mg /sub 0.9/ S:Eu(0.05 m/o), Ba(0.1 m/o), whose color coordinates are comparable to the red phosphor (Y /sub 0.964/ Eu /sub 0.036/ )/sub 2/O/sub 2/S, exceeds the latter in brightness by 15% at 18 kV excitation. Additionally, Eu/sup 2 +/-activated alkaline-earth binary sulfides are examined. A complete miscibility is ascertained in the pseudobinary system where the difference in cation radius is less than 0.035 nm. Stress-induced peak shifts are observed in MgS:Eu and A/sub 1//sub -/ /sub y/ B /sub y/ S (A or B is identical to Mg, Ca, Sr or Ba, A is identical to B). Some mechanisms for these shifts are proposed.

Cathodoluminescence of compositionally graded layers of GaAs1−xPx

Compositionally graded layers of GaAs1−xPx grown on (100) planes of GaAs substrates were investigated as a function of the distance t from the substrate, using a 77 °K cathodoluminescence technique. It was found that luminescence intensity L of these layers was strongly dependent on the profile of the compositional gradient, dx/dt. A number of the nonradiative recombination centers are three−dimensionally distributed in the shape of a cross−grid. This is related to misfit dislocations associated with impurities in the graded layers. The gradient dependence of L demonstrates that the density of these nonradiative recombination centers, N, is proportional to (dx/dt)2. This quadratic relation shows that only grading profiles which satisfy the condition d2x/dt2<0 can successfully decrease N continuously with increasing t. Discontinuous variations of x and/or dx/dt cause a significant degradation in the subsequent layers. From the spatial variation in the ratio of the intensity of the 1.35−eV band to the near−...

Autodoping Effects of Ge in Vapor‐Grown GaP Layers on Ge Substrates

The autodoping effects of Ge incorporated into the GaP layer grown via vapor‐phase transport on Ge substrate are investigated at 300°K. XMA and point‐contact‐breakdown techniques are used to obtain the free‐carrier concentration profiles across the grown layer. The free‐carrier concentration is found not to exceed 1.3×1017 cm−3 because of self‐compensation of Ge donor acceptors. The compensation ratio NA−+ND+ reaches up to 90% above 5×1017 cm−3 of |NA−+ND+|, where NA− and ND+ represent the ionized Ge acceptor and donor concentration, respectively. Considering various scattering mechanisms, ionization rates of the Ge atoms incorporated into the GaP layer are deduced. The emission spectra from zinc‐diffused p‐n junctions fabricated with these GaP layers also reveal strong dependence upon the Ge concentration. Their intensity variation is satisfactorily explained by the pair model. The correlation between the emission intensity of the Zn–Ge pair band and the injection efficiency of an electron is discussed a...

Role of diffused Ga vacancy in the degradation of vapor‐grown GaAs

Electron mobility, minority‐carrier lifetime, and misfit‐dislocation density are measured along the layer thickness direction near the interfacial regions of GaAs crystals grown on GaAs and Ge substrates by vapor phase epitaxy. It is observed that the mobility and lifetime decrease, while the dislocation density increases exponentially, as the layer thickness is decreased. These phenomena are found to be consistently caused by out‐diffusion of interstitial Ga vacancies introduced at the epitaxial layer/substrate interface in the stage prior to growth or in the first stage of growth. The diffusion coefficient of the interstitial Ga vacancy (off‐centered Ga atom) is estimated to be 3.6×10−5 exp(−11800/T) cm2/sec based on the experimental results.

Diatomic‐complex donor and acceptor model for Ge‐doped vapor‐grown GaAs

On the basis of thermochemical equilibria considering interactions between dopants and vacancies, the carrier concentration, electron mobility, minority‐carrier lifetime, and luminescence intensity, which have been measured as a function of the Ge concentration in a solid, are analyzed for Ge‐doped vapor‐grown GaAs. The quadratic dependence of the carrier concentration on dopant partial pressure is observed in Ge‐ and Sn‐doped GaAs and is reasonably explained by the hypothesis that the dominant donor is the diatomic complex formed between Ge or Sn substitutionals incorporated in the nearest‐neighbor Ga sites. For Ge‐doped GaAs, considering that the diatomic Ge donor and monoatomic Ge acceptor are dominant charged species in the extrinsic doping range, the measured electrical and optical properties are uncontradictorily explained with quantitative agreement. Using this double‐donor–double‐acceptor model, the origin of the space charges which significantly decrease electron mobility and the origin of minori...

Deformed layers observed at the interface between a Sn‐doped epitaxial layer and a Cr‐doped substrate in GaAs

Interfacial deformed layers existing in GaAs epitaxial wafers are conveniently observed on a {110} cleavage face by means of a room‐temperature photoetching technique with a slightly modified Abrahams‐Buiocchi etchant. Examination is mainly confined to vapor‐grown GaAs samples composed of an 0.4‐μ‐thick Sn‐doped epitaxial layer [n? (6–10) ×1016 cm−3] and a Cr‐doped semi‐insulating substrate. It is established that the deformed layer results from thermal stress imposed on the arsenic depletion layer generated at the substrate surface in the preheating stage prior to growth. The strain field is found to extend more than 10 μ into the substrate side and even into the epitaxial layer side. Electron mobility in the submicron epitaxial layer is lowered by the presence of this strain field. However, this can be improved from 10 to 30% by annealing. It is also found that dislocations are generated in the deformed layer when the imposed stress is increased by coating the back side of the substrate with a SiO2 film...

Autodoping effects of Ge in vapor-grown GaAsl-xPx layers on the Ge substrates

Epitaxial growth of GaAs1-xPx layer on the Ge substrate has been investigated under the optimized growth conditions for reducing vapor etching of the substrate, using a Ga-PCl3-AsH3-H2 system. The free carrier concentration, ⊢ND+−NA−⊢, and the electroluminescent properties of GaAs1-xPx layers with x ⋍ 0·4 are studied, and are correlated with the Ge concentration involved. In the lightly doped region below 1×1017 atoms/cm3, bright electroluminescence is observed at room temperature from forward-biased p-n junctions fabricated by a zinc-diffusion technique. However, in the narrow region of 1×1017−4×1017 atoms/cm3, the enhanced amphoteric behavior of Ge leads to concentration quenching of visible-light emission. The ⊢ND+−NA−⊢ reaches its maximum at ∼ 1×1017 atoms/cm3. Nearly complete self-compensation is observed above 4×1017 atoms/cm3 due to the increase of the concentration of deep-lying Ge acceptors.

Regular compositional steps generated in GaAs1−xPx VPE layers

For GaAs VPE layers grown on Ge substrates, it is found that a one‐dimensional misfit‐dislocation density 1/p is proportional to lattice constant mismatch, just as for compositionally graded GaAs1−xPx layers grown on GaAs substrates. On the basis of these experimental results, lattice constant variation due to compositional change is given in a form explicitly including a compositional step. The compositional step width, calculated from this relationship and observed dislocation density, is about 500 atomic layers. Regular compositional steps, which are unintentionally formed, are actually observed on A‐B etched cleavage planes of the graded layers. The observed width of this step is about 0.3 μm. This value roughly agrees with the calculated one. Presumably, the discontinuous change in composition is caused by competition between the following two processes which alternately dominate GaAs1−x Px epitaxial growth: a free‐energy increase due to a decrease in arsenic supersaturation in vapor phase and a free...