To export a background PNG as an HD vector, you can use the @react-native-vector-icons package in combination with Expo. Here's a brief snippet to get you started:

import React from 'react';
import { Feather } from '@expo/vector-icons';

const Background = () => {
  return (
    <View style={{ width: 300, height: 400 }}>
      <Feather name="sun" size={64} color="#fff" />
    </View>
  );
};

export default Background;

In this example, we're using the Feather icon from @expo/vector-icons, which is a wrapper around react-native-vector-icons. We can then export the component as an HD vector by setting the size prop to a high value (in this case, 64).

To achieve an HD vector, you'll need to use a tool like Adobe Illustrator or Inkscape to create your icon at a high resolution. Then, you can import the PNG file into your React Native project and use it as a background image.

Alternatively, you can use a tool like mermaid to generate SVG code from your design. For example:

import mermaid from 'mermaid';

const svg = `
  +---------------+
  |               |
  |  Sun Icon    |
  |               |
  +---------------+
`;

export default () => (
  <View style={{ width: 300, height: 400 }}>
    {mermaid.render(svg)}
  </View>
);

In this example, we're using the mermaid library to generate an SVG code from our design. We can then export the component as an HD vector by setting the width and height props accordingly.

Note that these examples are just a starting point, and you may need to adjust the code to fit your specific use case.