Measurements of intervalence band absorption spectra were made in p-type In 0.53 Ga 0.47 As, InP, and GaAs. The measured spectra are broader, have less temperature dependence, and have 2× less peak intensity than theoretical curves predicted by an elementary k\cdotp band model. For p = 10^{18} cm-3, all three crystals have absorption coefficients of about 13 cm-1at 1.3 μm and 25 cm-1at 1.6 μm. These values of absorption should also be applicable as estimates of intervalence band absorption in quaternary laser material. Because of the low strength and weak temperature dependence of the intervalence band absorption, it should have only a minor effect on the temperature dependence of laser threshold. For example, using our absorption data, we calculate that intervalence band absorption will reduce the experimental temperature parameter T 0 of 1.3 μm quaternary lasers from 194 to 179 K.

The effect of intervalence band absorption on the thermal behavior of InGaAsP lasers

The temperature dependence of the threshold current of GaInAsP/InP lasers was considered in terms of linear gain, loss, and carder lifetime. The linear gain was calculated taking into account electronic intraband relaxation effects. The carrier lifetime, intraband relaxation time, loss in the active region, and dipole moment, all of which determine the threshold condition, were estimated from the experiments. The main loss mechanism which determines the temperature dependence of the differential quantum efficiency appears to be the absorption due to transitions between the split-off and heavy-hole valence bands. The temperature dependence of the theoretical threshold current I th calculated in terms of these parameters was compared with the measured results and reasonable agreement was obtained.

The temperature dependence of the threshold current of GaInAsP/InP DH lasers

Chapter 5 – heterostructure materials

The contact properties of various metal combinations, deposited by vacuum evaporation on InP, were studied. Among these metal combinations, Au/Ge + Ni and Au/Zn proved to be most suitable. The former on n-InP (n = 8 × 1017/cm3) and the latter on p-InP (p = 9 × 1017/cm3) exhibited specific contact resistances as low as 1.2 × 10−6 and 1.1 × 10−4 Ωcm2, respectively. The specific contact resistances were analyzed using a four-point method which also accounts for the spreading resistance. Furthermore, the resistances of metal contacts to InP were calculated as a function of doping concentration and were compared with the experimental results. The described contacting technique was successfully applied to the preparation of quaternary lasers.

Low resistance ohmic contacts to n- and p-InP

InGaAsP/InP buried‐heterostructure lasers with a stripe width of 1–2 μm have been fabricated by two‐step liquid phase epitaxy and preferential chemical etching. They operate in the fundamental transverse mode at wavelengths of ∼1.3 μm with threshold current as low as 22 mA. The temperature limit for cw operation is 80 °C.

Fabrication and characterization of narrow stripe InGaAsP/InP buried heterostructure lasers

In 1-x Ga x As y P 1-y /InP double heterostructure (DH) laser diodes with emission wavelengths of 1.25-1.35\mu m at room temperature were fabricated on

Y. Suematsu

Papers

In 1-x Ga x As y P 1-y /InP DH lasers fabricated on InP