Terraced Substrate Research Articles

Surface and step magnetic anisotropy.

Cu(11n) surfaces vicinal to Cu(001) are characterized by (001) terraces separated by monoatomic steps. Growth of thin epitaxial magnetic films on such terraced substrates, e.g., Co/Cu(1 1 13), leads to unexpected magnetic anisotropy associated with the surface steps. This anisotropy remains largely unexplained, and is of potential technological importance. We have studied the anisotropy of fcc Co/Cu (1 1 13) films using in-situ magneto-optical Kerr effect (MOKE), and find an in-plane uniaxial anisotropy favoring magnetization parallel to the steps. The strength of this anisotropy decreases with increasing film thickness. In this paper we focus on the interpretation of this anisotropy in terms of the N\'eel model. The N\'eel anisotropy energy for such a film has the form ${\mathit{E}}_{\mathrm{film}}$= ${\mathit{E}}_{\mathrm{bulk}}$-2${\mathit{E}}_{\mathrm{surface}}$/t-2${\mathit{E}}_{\mathrm{step}}$/(td), where t and d are film thickness and terrace width, respectively. The last term includes contributions from sites at both the upper edge and inner corner of the step and makes the dominant contribution to the step-induced anisotropy. This model properly accounts for the preferred direction of magnetization parallel to the steps in Co/Cu(1 1 13). bcc Fe/W vicinal to (001) shows a preference for in-plane magnetization perpendicular to the steps for t2.5 monolayers. The N\'eel model also predicts this anisotropy for a bcc Fe film provided the magnetization lies in the film plane, not in the (001) plane.

Ga<inf>x</inf>In<inf>1-x</inf>As<inf>y</inf>P<inf>1-y</inf>/InP terraced substrate single-mode laser

An index-guiding structure capable of providing well-controlled single-mode operation has been realized for Ga x In 1-x AS y P 1-y /InP lasers ( x = 0.28, y = 0.62 , and \lambda = 1.3 \mu m) using a terraced substrate (TS) configuration prepared by single-step LPE growth. The threshold current was reduced to as low as 44 mA and single-transverse and longitudinal mode operation was stably achieved up to 2.8 times the threshold. Continuous operation at room temperature was also demonstrated.

Reduction of threshold current in GaAlAs terraced substrate lasers

An improved structure of a terraced substrate (TS) laser is presented. The injected current distribution is calculated and compared with that in a conventional TS laser. It is shown that 90 percent of the total current is injected in a filamentary stripe region between the two bends of the active layer by the improved structure. A TS laser with a very low threshold current of 12 mA is obtained at a cavity length of 120 μm under continuous operation. Output powers obtained by the TS laser with and without a facet coating are 70 and 40 mW per facet, respectively. The improved TS laser shows both stable fundamental and longitudinal mode oscillations as in the conventional TS laser. The operating time of TS lasers is estimated to be more than 2 \times 10^{5} h at room temperature from the result of accelerated life tests at the high temperature of 70°C.

Very low threshold visible TS lasers

Fundamental transverse mode lasers with very low threshold currents have been realized by use of the modified terraced substrate (TS) geometry. The threshold currents of 250 μm cavity length lasers at room temperature are typically 20-30 mA for wavelengths around 750 nm. In the 710 nm laser, which is the shortest lasing wavelength in this work, the threshold is as low as 70 mA in CW operation. The 726 nm laser was operated for only 150 h, while a lifetime longer than 10 000 h is expected for TS lasers with a lasing wavelength longer than 750 nm.

Single Transverse Mode Operation of Terraced Substrate GaInAsP/InP Lasers at 1.3 µm Wavelength

GaInAsP/InP terraced substrate (TS) lasers (λ=1.3 µm) have been fabricated and stabilized single transverse mode operation has been demonstrated. The wafers were prepared by a single-step LPE growth on (100) n-InP terraced substrates which was terraced along <011> orientation. Pulsed threshold current was less than 50 mA at room temperature. Single transverse and longitudinal mode operation was obtained up to 2.8 times the threshold. Cw operation was also achieved at room temperatures.

Visible-Light-Emitting TS Lasers

Some characteristics of (GaAl)As TS (Terraced Substrate) lasers which emit visible radiation are reported. The threshold current density is found to depend little on the lasing wavelength down to 740 nm. The lasers exhibit a stable, single longitudinal mode oscillation with no kinks in the output-current curves over a wide range.