Improving optical transparency in CdGeAs2 crystals by controlling crystalline defects

Preparation and characterization of CdGeAs2 crystal by modified vertical Bridgman method

“…6(b) shows the plot of calculated absorption coefficient (a) versus wavelength. It shows that the alpha at 1818 cm À 1 (5.5 um) was 0.42 cm À 1 , which is very close to the best report in earlier work [13]. Now more optimized growth conditions and the post-treatments such as annealing and electron beam irradiation are in the process of being studied to further improve IR transmission and the optical homogeneity for device fabricating.…”

“…[6,7], among the polycrystallites; secondly, CdGeAs 2 crystal has a huge thermal expansion anisotropy [8] (almost 15 fold difference between a-and c-axes), which makes the as-grown crystal extremely crack at the step of cooling; thirdly, the constitutional super-cooling [9] leads to a tendency towards polycrystalline. Up to now, a number of crystal growth techniques, including vertical Bridgman [10] (VB), chemical vapor transport method [11] (CVT), float zone [12] (FZ), and horizontal gradient freeze technique [9,13] (HGF), which have been well developed in recent years have been utilized to grow CdGeAs 2 single crystal; however, still some problems exist such as cracking, polycrystallinity in VB, and extra phase at rear part of crystal in FZ and HGFT. In addition, the oxygen contamination and inhomogeneous nature of the starting materials in synthesis process would lead to heavy optical absorption and deviation.…”

Correlation between dislocation etch pits, carrier concentration and optical absorption in CdGeAs 2 grown by modified Vertical Bridgman method

“…Unfortunately, there is a harmful absorption in the region of 5.5 µm varying not only from one laboratory to another, but also from boule to boule and within each boule (across the boule's radius and along its length) [15], which has further limited its usefulness, such as reducing the SHG efficiency at the doubling wavelength for the 10.6 µm CO 2 laser [10,16] and laser output power of optical parametric oscillator (OPO) [17][18][19]. This absorption is attributed to the intraband transition between the two upper valence bands [20][21][22] and it's suggested that the defects responsible for the shallow acceptor may be associated with germanium on arsenic sites (Ge As ) by electron paramagnetic resonance (EPR) measurements [23].…”

“…And the interaction of dislocations with other types of defects in crystals has been thought to play some role in the electrical and optical properties. K. Nagashio et al focused on the influence of dislocation density and optical absorption at 5.5 µm, and discussed an improvement by alteration of the growth orientation [5,15,24]. Lihua Bai et al established a linear correlation between absorption at 5.5 µm and hole concentration [25,26].…”

Effect of thermal annealing on the optical properties of CdGeAs2 wafers

“…It is characterized by one of the highest non-linear optical coefficient (d 36 ¼236 pm/V) of any known compound, wide transparency range of 2.3-18 mm, sufficient birefringence (n e À n o E0.09) and relatively high thermal conductivity (about 42-93 mW/cm K) for high average power applications [1][2][3][4]. So this material is very attractive in second harmonic generation (SHG) [5] and optical parametric oscillator (OPO) device fabricating and has bright future in mid-and far-infrared regions applications [6].…”