We measure drift velocity in monolayer graphene encapsulated by hexagonal boron nitride (hBN), probing its dependence on carrier density and temperature. Due to the high mobility (>5 × 10⁴ cm²/V/s) of our samples, the drift velocity begins to saturate at low electric fields (∼0.1 V/μm) at room temperature. Comparing results to a canonical drift velocity model, we extract room-temperature electron saturation velocities ranging from 6 × 10⁷ cm/s at a low carrier density of 8 × 10¹¹ cm^–2 to 2.7 × 10⁷ cm/s at a higher density of 4.4 × 10¹² cm^–2. Such drift velocities are much higher than those in silicon (∼10⁷ cm/s) and in graphene on SiO₂, likely due to reduced carrier scattering with surface optical phonons whose energy in hBN (>100 meV) is higher than that in other substrates.

中文翻译：

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六方氮化硼包裹的石墨烯中的高饱和度

我们测量了六方氮化硼（hBN）封装的单层石墨烯的漂移速度，以探究其对载流子密度和温度的依赖性。由于我们样品的高迁移率（> 5×10 ⁴ cm ² / V / s），室温下低电场（〜0.1 V /μm）时漂移速度开始饱和。将结果与标准漂移速度模型进行比较，我们提取了室温电子饱和速度，在8×10 ¹¹ cm ^–2的低载流子密度下，范围为6×10 ⁷ cm / s，而在较高的载流子密度下，则为2.7×10 ⁷ cm / s密度为4.4×10 ¹² cm ^–2。这样的漂移速度比硅中的漂移速度高得多（〜10 ⁷（cm / s）和SiO ₂上的石墨烯中，这可能是由于表面光子的载流子散射减少所致，后者在hBN（> 100 meV）中的能量高于其他衬底。