Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Fast multicolor photodetectors based on graphene-contacted p-GaSe/n-InSe
  van der Waals heterostructures   The integration of different two-dimensional materials within a multilayer
van der Waals (vdW) heterostructure offers a promising technology for realizing
high performance opto-electronic devices such as photodetectors and light
sources1-3. Transition metal dichalcogenides, e.g. MoS2 and WSe2, have been
employed as the optically-active layer in recently developed heterojunctions.
However, MoS2 and WSe2 become direct band gap semiconductors only in mono- or
bilayer form4,5. In contrast, the metal monochalcogenides InSe and GaSe retain
a direct bandgap over a wide range of layer thicknesses from bulk crystals down
to exfoliated flakes only a few atomic monolayers thick6,7. Here we report on
vdW heterojunction diodes based on InSe and GaSe: the type II band alignment
between the two materials and their distinctive spectral response, combined
with the low electrical resistance of transparent graphene electrodes, enable
effective separation and extraction of photoexcited carriers from the
heterostructure even when no external voltage is applied. Our devices are fast
(< 10 {\mu}s), self-driven photodetectors with multicolor photoresponse ranging
from the ultraviolet to the near-infrared and have the potential to accelerate
the exploitation of two-dimensional vdW crystals by creating new routes to
miniaturized optoelectronics beyond present technologies.

5
The categories of this paper are: gr-qc
9
The categories of this paper are: nlin
0
The categories of this paper are: hep-ph
6
The categories of this paper are: astro-ph
29
The categories of this paper are: funct-an
31
The categories of this paper are: ao-sci
1
The categories of this paper are: cs
12
The categories of this paper are: nucl-th
30
The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
13
The categories of this paper are: quant-ph
32
The categories of this paper are: atom-ph
20
The categories of this paper are: acc-phys
33
The categories of this paper are: plasm-ph
36
The categories of this paper are: cmp-lg
7
The categories of this paper are: hep-th