HARPIA-TG 是一种瞬态光栅光谱仪，用于测量扩散系数和载流子寿命。测量基于激光诱导的瞬态光栅（LITG）技术，该方法通过全光学手段同时观察非平衡载流子复合和扩散。HARPIA-TG 可用于表征电气非导体或非荧光样品。它适用于半导体材料和衍生物，例如碳化硅（SiC），氮化镓（GaN），钙钛矿，有机和无机太阳能电池，量子点甚至复杂的纳米结构，如量子阱。

应用

瞬态光栅光谱学
单波长的瞬态吸收

Basics of Operation

The principle of a LITG measurement is depicted in the figure on the right. A pair of ultrashort pulses are overlapped both spatially and temporally at the sample plane. Angular separation of the excitation beams causes them to interfere at their crossing. The period of the interference pattern Λ depends on the beam intersection angle and the pump wavelength.

Excitation by a periodic pattern creates a spatially-modulated excited carrier distribution and, effectively, a periodic modulation of the refractive index. Therefore, this pumping geometry produces a transient grating from which a temporally-delayed probe pulse can diffract. Over time, the laser-induced grating decays due to carrier recombination (electronic decay with the rate of τ_R) and carrier diffusion (spatial decay with the rate of τ_D ). The diffusion term depends on the transient grating period: fine gratings (small Λ values) diffuse faster than coarser ones (large Λ values).  Accordingly, if we measure the temporal behavior of the diffracted signal over a series of different periods Λ, we can determine the carrier diffusion coefficient D[cm²/s] from the relationship,

where τ_G is the net decay rate of the transient grating.

测量范围

Parameter	Value
扩散系数	0.1 – 50 cm²/s
载体寿命	1 ps – 80 ns

Measurement Process

I.

Transient decay dynamics are measured at various grating periods Λ. HARPIA-TG allows continuous tuning of the excitation grating period. Periods ranging from 1.15 to 15 μm (depending on the pump wavelength) can be formed at the sample plane.

II.

Data obtained at each grating period is fit to an exponential decay. The retrieved reciprocal decay constants are plotted
as a function of the inverse square of the grating period. Tangent of this curve provides the carrier diffusion coefficient (at the given carrier concentration and temperature), while the zero-intercept point (Λ = ∞ μm) provides the intrinsic carrier recombination rate τ_R.

III.

Experiment is repeated at various excitation intensities to obtain a comprehensive dependence of the diffusion coefficient on the non-equilibrium carrier concentration.

Polarization and pump wavelength control enables more advanced spin grating and thermal grating measurements, respectively.

规格参数

型号	HARPIA-TG
光栅记录 ¹⁾	340 – 560 nm
探测波长 ²⁾	1030 nm
光栅周期 ³⁾	1.15 – 15 μm
脉宽	< 290 fs
延迟范围	高达 8 ns

可扩展至长波（可见光/近红外）。详情请联系 sales@lightcon.com。
可根据需求提供 SH(515 nm)或基于 OPA 的探测。详情请联系 sales@lightcon.com。
取决于激发波长。

测量范围

型号	HARPIA-TG
扩散系数	0.1 – 50 cm²/s
载体寿命	1 ps – 80 ns

外形尺寸

型号	HARPIA-TG
尺寸 (长 × 宽 × 高)	730 × 420 × 188 mm

性能

The graphs below indicate the carrier diffusion coefficient, diffusion length, and lifetime of GaN at the back and at the front of the layer as a function of fluence. The thicker the GaN, the better the quality of the grown layer due to better coalescence. It is evidenced by the lower diffusivity and shorter lifetimes that indicate poor structural quality and higher defect density at the interface between the sapphire substrate and GaN.

Measurements were performed using HARPIA-TG combined with CARBIDE-CB5 laser and I-OPA. Measurement conditions: 60 kHz, 355 nm pump wavelength, 1030 nm probe wavelength.