Effect of Induced Strain Due to Lattice Mismatch between Mg_yZn_1-yS Cladding Layers and Cd_xZn_1-xS/ZnS Quantum Wells on Effective Band Gap Energy in Cd_xZn_1-xS/ZnS/Mg_yZn_1-yS Separate-Confinement Heterostructures

Abstract

The improvement of selectivity for polysilicon (poly-Si) etching without lowering the selectivity to SiO 2 is possible through the implementation of time-modulation (TM) bias. RF bias (800 kHz) applied to a substrate in an electron cyclotron resonant (ECR) etcher is pulse modulated with a repetition frequency of 1 kHz. The amplitude of RF voltage controls the energy of the ions accelerated toward the wafer. The flux of accelerated ions is controlled by the duty ratio of the pulse. The taper angle of the sidewall of line patterns is 89 • for TM bias and 81 • for conventional continuous-wave bias. The etch rate of the poly-Si is ∼300 nm/min and has a selectivity to SiO 2 of 17. In addition, microtrenching at the bottom of the space is suppressed by the implementation of TM biasing. Modeling of the etch profile based on the competition of deposition and etching on the sidewall surface can explain the effects of TM bias.

Proposal for ZnS/MgxBeyZn1-x-yS Quantum Wells

“…33,34) We used C ZnMgS ¼ 0:0698 eV because of a recently reported value. We used parameter sets for BeS 6,7,35) and MgS 18,33) reported recently. Therefore, the values 0.481 nm and 5.39 eV were used as the lattice constant and band gap energy in BeS, respectively, while we use 0.5615 nm and 5.1 eV as the lattice constant and band gap energy in MgS, respectively.…”

“…In a previous study, we expected that a MgS/ZnS heterostructure would have a negative valence band offset (VBO) under no induced strain condition using Harrison's atomic orbital (HAO) without taking into account the effect of d-states. 18) However, ZnS/MgZnS single quantum wells (SQWs) were fabricated and exhibited type-I band lineups. 17) In this study, we estimate the top valence band in ZnS using HAO by taking the effect of d-states 19) into account.…”

Effect of Induced Strain on Band Lineups in CdxZn1-xS/ZnS/BeyZn1-yS Separate-Confinement Heterostructures

“…With increasing y, E g,clad À E g,barrier increases, because z increases with increasing y. The increase in E g,clad À E g,barrier is larger than that in Cd x Zn 1Àx S/ZnS/Mg y Zn 1Ày S SCHs, 6) because the band gap energy of BeS is larger than that of MgS.…”

“…Therefore, SCHs are useful in designs for the fabrication of light-emitting devices. We calculated that the induced compressive strain in a Cd x Zn 1Àx S well layer is reduced using a Mg y Zn 1Ày S cladding layer, 6) because the lattice constant of the Mg y Zn 1Ày S cladding layer is larger than that of the ZnS layer. 3) The decrease in induced compressive strain affects the conduction and valence band offsets.…”